I apologize if this topic has been done…but…I still am using 2.49b because I do production and did not want to put all the time needed into learning the new interface until it was stable enough for paying work.
Is it?
Thanks, anyone who answers.
It should be… they made 12 minutes long movie with it… and found an corrected several hundreds of bugs in the meanwhile… from my experience, Blender 2.56 (and 2.55) has never crashed. Python api is almost final, but that shouldn’t be the problem unless you use custom python scripts in your work-flow.
Thanks! I am so ready for 2.5!..I jumped into it when it first came out but soon realized that I needed to make a choice, and have been patiently waiting to go to 2.5 while using 2.49b…I think it’s time.
There is a lot of stuff not re-implemented at all or not implemented properly yet.
So I´d go with a:
Maybe…
If you aren´t needing anything from this list:
http://wiki.blender.org/index.php/Dev:2.5/Source/Development/Todo
You’r good to go with 2.5.
It really is painfully, 2.5 being beta, and the term includes “not meant for production yet” but the craving to use it once you tried it is too big 
Blender 2.5 has seen a lot of fixes just this month alone and that being around or after the time 2.56 beta was released.
A lot of crashers being fixed, code cleanup, re-organizing, speedups, todo items, RNA API work, and more general fixes.
Ton even just fixed the problem with bumpmaps and soft buffer shadows not showing up in raytraced reflections and refractions (which were two of the biggest bugs in the Internal Render Engine)
Todo should be done in March/April, so you can start learning the new UI right now.
I would agree with Raub, start using it now, just to get a feel for it, however I might wait with the very heavy production stuff for a month or three.
It is ready for caotic production at the moment.
Before any production you should anyway test all features you intend to use, whatever the soft is, so, up to you …
All productions help a lot improving blender stability, much more than cube testing !
Juste as Bao2 wrote: KADRI short (less than 6 min.) done last year mostly with 2.5x.y.z Betas…
P.S. @delic: Lausanne is about 20km from my home!.. 
if you use 2.49 and are already fluent with it than I think it takes about a week tops to learn the 2.56 interface its different but its not that radically different.
The 2.5 UI is really easy to learn, I’m not sure how it is if you are already used to 2.49 but it took me about a day to get familiar with 2.5 when I first started.
can someone post what was fixed with the bump? before that i never had any problems with bump
It was to do with ray-traced reflections not rendering bump mapping and/ or blurred shadows, something I hadn’t noticed, but is indeed a major bug.