< Obsolete post that has no more relevance >
For me, I’ve been using blender since 2.37 and 2.5 feels like the best user experience for me by far. 2.5 is a winner, 100% for me.
I had tried Blender from time to time, but the user interface was such a big stumbling block that I never got to use it longer than an hour.
With 2.5 that has completely changed. The new interface is so well thought-out that it instantly made sense. I gues for the vast majority the new interface is a big relief 
Greetings from Germany!
I can garantuee that the 2.49 interface won’t be back. You just have to accept it, and I think you will grow to like it the more you use it. In my opinion the 2.5 interface is a huge inprovement even though there’s room for improvements.
I don’t agree the interface has changed completely. The basic button layout has changed from horizontal to vertical but the basic workflow I don’t think has basically changed. While the old interface had evolved over many years with the problem that all logic had gone out of the window as to what button was where. With 2.5 there has been the opportunity to lay these out in a clear logical manner.
The scrolling and the bulky Buttons are
the hardest critique points on 2.5 definetly. In 2.49 you had all
you need in one view, had a very big workspace above and still
enough space to add a UV-ImageEditor and an Outliner. But now, all
the space is blocked by the new ‘eyecandy’ buttons.
The interface takesadvantage of the more modern widescreen type display which the old interface didn’t make sense with. If you don’t have a wider screnn then tough, you’ll have to readjust the widows. You dont need the tool shelf anyway, either use the menus or space (search) and F6 floating panel
The feeling of depth in the 3d window has definetly become another
adventure, it looks very irrealistic (much to hard depth).
Another thing to worry of is the new Camera movement by using the
Numpad. You have a fly to feeling when you switch, which can
definetly help to navigate over the model and helps to keep the
dimensions. But theres a dark side about the ‘flyswitchcam’ which
is the flying over highpoly, massive particle or physics scenes. It
laggs some computers completely to switch the view in scenes like
this.
Not seen any issues myself
Then the new Buttons for e.g. Shading(F5), they were easy to
understand earlier, but now you even have to scroll those buttons and
the new design seems like windows 7. Glossy and useless big. Overall
i would say that the GUI is a step back from serious development.
Windows 7?? See my earlier response. ‘step back from serious development’ , not sure what you mean by this.
I really hope there WILL be an official build with the old interface
aswell in 2.6 because i know hundreds of people having the same
problems like me.
Don’t get your hopes up, unfortunatly for you and these supposedly hundreds of people, 2.5 is the future whther you like it or not. As the interface is all python based that gives the opportunity for you or some 3rd party to create an alternate layout, if they think the effort is worth it.
In my experience I don’t find the changes that difficult to adjust to. Give it an hour and you’ll know what is where or if not where it is logical to find it.
I didn’t use 2.4x much. I stopped using Maya and preferred Blender 2.5x because Blender has improved UI and robust tools.
Honestly, I wouldn’t prefer 2.4x if 2.5x series didn’t released.
I’ve been using blender since the 2.47, so not very long compared to most of the people here. In my opinion the 2.5 interface is by far an improvement over the 2.4. In my job I’ve had to use many different CAD programs. In the end it’s just a matter of getting used to how to use the program. It grows on you.
That is also in 2.49, but you have to turn it on. Now its just on by default and you can turn it off 
the only thing i don’t like in 2.5 is: when you try to arrange the properties / buttons frame on the bottom such as in the default 2.49 view - you’ll have about 10cm from the left side just empty space before the option panels start (although arranged horizontally…). This is the most ridiculous thing ever and really looks ugly.
it wasn’t really meant to be used horizontally, if memory serves me right the first design documents proposed killing the horizontal style layout. There was a lot of protesting about this ( do a search you can find the thread), so this ugly compromise was reached. It only takes one brief look to see that this new design mode doesn’t work horizontally.
Most computer screens are now in 16:9 ratio and if you have one of those 4:3 ratio screens come on upgrade. I live in a country that slaps on about a 30% import duty on electronic before VAT and screens are cheap. On a 16:9 screen vertically layout tramps the horizontal one.
Go vertical and live with it.
I for one absolutely love 2.5 
I started out with 2.47 in 2008, and although I loved the way it worked back then, I find 2.5 much, much better. just the way it looks really helps, and everything is much more organized…
…and the Search option is just awesome!
i do agree though that the fly-to camera thing can slow everything down sometimes…even though it’s less confusing, it can be annoying at times.
the only other thing I find disappointing about using it (at least, that I can think of at the moment) is the fact that I can’t open external windows, 'cause the text goes bezerk…but it has nothing to do with Blender, it’s my laptop’s crappy video card. 
but still, it limits what I can do with the program…
i remember when I tried it for the first time, I was completely lost, but after a few days I found most of the tools…still finding some “new” features (new because I’ve never used them before), but overall it didn’t take long to adjust.
I did notice the horizontal text-thing though - and in my case the entire Properties Window went nuts, and pretty much crashed, so I stopped trying to have the classic interface… I actually have 2.49b set up similar to 2.5 now, lol
can’t wait to see a final 2.5… BIG THANKS (haha, literally too) TO THE DEVS! 
This is indeed a problem for long time users. There is no way around experiencing some pain when big changes are made but in the end it should make work easier.
Just to make sure you know, you can adjust the size of the user interface elements by Ctrl + Middlemouse draging. This won’t solve all your problems but maybe some of them.
This is not a new feature but just a new default. If you look in the user preferences there is a “Smooth View” variable (under “Interface” in 2.5 and under “View & Controls” in earlier versions). If you set this to 0 there will be no more transitions on camera changes.
I don’t quite understand what you mean by that could you elaborate?
I can use it good.
Heh, that’s been driving me batty for a while now… but now I know how to turn it off.
Me poor video card just wasn’t up to the task with >30k verts apparently.
I want to completely agree with this, and have little sympathy for jimmyons massive moan. Good thing a whole heap of oldskool 2.49 (and lower) users are really digging 2.5. What i would like to know is why some people still use 2.49 etc, for scripts and missing features? 2.5x is still alpha and undergoing extensive testing/fixing, relax bro 
I’ve been using blender since 2.4/2.42, and also like the 2.5 interface better… Everything feels faster to use, even with the new shortcuts… 
-c-
edit:
Coming from 7-8 years of max-use, i feel that blender has really come on-par with the big packages. I would prefer Blender’s modelling tools, and the 2.5 interface over max’s any day… And i used to model in 3dsmax almost every day for all those years…
Ive been using Blender 2.4x for some while.
When i switched to 2.5, i was amazed how good it was, i fell in love with it at the first glance.
Sure, at the beggining “Where did the button x go?” was present… but it went away in a day or two, because the new gui makes so much more sense…
Blender 2.5 interface is just better in almost every way, Imho.
Some things I still find missing in the GUI though, like floating panels and horizontal layouts… I’m not a fan of the toolshelf, really…
ok. i reread your post and deliberated a bit. By this point a lot of your 2.5 criticism has found a solution or satisfactory clarification. Quite a bit of your apprehension towards 2.5 stems from a very quickly manifested resistance.
Maybe you can now rewrite your original post removing the “you cants” and the taste of learned helplessness. Also, give some screenshots of how this interface change has impacted your workflow. I’d like to understand you.
Haven’t read everything, but for now I can just say that your point about F5 it’s completely wrong. In 2.49 moving from the shader panel to the texture panel looked like a not seamless step, they looked like different things not related to each other, maybe due to the thing that by default they were laid horizontally, but besides that the buttons and the panels were like unrelated to each other. Also, everything now is more coherent. 2.5 is a big step forward about the user interface.
Just to make sure you know, you can adjust the size of the user interface elements by Ctrl + Middlemouse draging. This won’t solve all your problems but maybe some of them.
Awesome! completely solves the above mentioned to much scroll issue. Thanks!!
Lazer