What’s the most frustrating and/or annoying aspect of doing any 3D artwork?
Fixing all those little things.
I would say sketches, just becuase it’s the longest process, and the most important. For me, there seems to be a lot of pressure to get it all figured out right before I start working.
Lighting, because Blender doesn’t have a real-time, OpenGL preview.
(but Maya does)
Completely depends on the project. On some occasions the modeling is the most difficult part, but it depends on what you’re trying to model. Sometimes coming up with an idea is the most difficult part, whereas other times you already know exactly what you want.
But I seem to have the most difficult time finding/creating good references. So that’s what I voted for. 
Getting the Scene lighting to sit comfortably with Materials/Textures and shadows.
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Very true, but I think texturing (UV) is the toughest for me, which fits in with what you are saying. Texturing makes or breaks a model, but with me it tends to break more. :x
-Laurifer
I personally voted lighting.
I find quite often that you can get a material looking semi decent and then with one flip of a switch or nudge of a slider, the lighting will screw the entire look you wanted.
I also think that lighting can be the most difficult to understand. So many light types, what set-up to use. Throw in Yafray to the equation and you’ve got a whole heap of trouble.
I don’t think CG lighting is anywhere near as “user-friendly” as say materials or modelling tools.
Just my opinion really 
It’s a tough one. I would be tempted to go with modelling, rigging and animating as the most frustrating. The reason would be not because they are the most difficult but once you reach a certain point, fixing mistakes becomes impossible. For stills, I would say lighting is most important and so probably most frustrating.
The animation stage is really time consuming and making minute timing errors could mean you have to scale loads of IPOs again and again.
I would say lighting and UVmapping are pretty hard to do and are essential to get just right but you can change them at any time so I don’t think they are quite as frustrating.
If you know about studio lighting then it shouldn’t take long to sort your lighting out.
In summary, I feel that all of the 3D process is frustrating and the most frustrating parts are just the bits you are worst at. That’s why it’s so hard to do good work on your own - you have to be a good concept artist, modeller, rigger, animator, lighting artist, texture artist and even compositor all by yourself.
doing the job in a way blender allows me to.
as much as i love blender often i have to use
a different render engine because blender still
lacks some elements i need for my work.
second are missing nurbs tools.
claas
For me, it’s the conceptual stage. I can’t think of what I want to model, so I try to make a sketch. Then, I realize that I can’t draw worth a crap, so I go back to modelling…[etc]
The hardest part for me is the cinematography.
In a CG project of any size you have to do everything backwards… designing the project, setting up all the camera angles and all the shots, in effect doing all of the final-editing, almost entirely on your imagination. Before you actually render anything final. Even an animatic is expensive and time-consuming.
The temptation is to “rush to final,” to do something.
And … if you need to do realistic human movement, no matter how short, oh, Lord how difficult that is for me! Much more difficult than I think it has any right to be. I feel that I ought to be able to grab “an actor” out of a box, plop him into the scene, tell him to hit this point on beat #43 and that point on beat #101 while realistically carrying this 100-pound implement in his arms, and the computer ought to be able to grind away for a while and come up with that movement for me. Blender seems to have nothing, nothing, NOTHING! in this area… 
I can’t even get decent movement, much less a performance.
I’m going to experiment with BVH files before I even attempt manual human character animation. One major problem I find is with IK controls. I find them really hard to control and there are times when it’s essential to use FKs - IKs just don’t bend certain ways. I don’t think Blender has an IK/FK switch like some other software so it becomes a bit of a pain.
But IK’s are almost essential for getting characters to grab things. I’m thinking you could maybe make an empty and attach it to the wrist and use a script link to get it to move the arm like an IK chain and when you use FKs, the empty just sticks at the wrist so that way you get the best of both but I’m not sure how easy it will be yet.
You can download loads of BVH files online. Blender has an import script for them:
http://www.centralsource.com/blender/bvh/files.htm
http://www.bvhfiles.com/index.htm
Just load one close to the motion you need and adjust the IPOs.
I would have put Animating on the poll list but once I’d made my vote, it locked me out of changing the possible answers %|
With regard to IK/FK setups. I think obviously that both have their merits. I know that for each IK bone you can change the INFLUENCE slider for the IK control which is very similar to having an IK/FK blend (rather than a straight on/off switch.)
A good example of having a blend IK/FK is if a character is approaching a set of stairs and reaches out to grab a handrail. It’s all FK up until the grabbing point and then you gradually introduce the IK target to lock the arm onto the rail.
It’s hit and miss.
I do agree that getting a performance out of a CG character/Rig is very difficult.
I’ve been trying to get the Project Orange sample guy to dance in time to some reference footage and it’s a nightmare to get good movement.
On the flipside, with shape keys etc… now, facial animation I reckon is MUCH easier than it has been and that’s a big bonus since a lot of character comes through the face.
My original vote was lighting and it still stands but a very close 2nd is the animating process.
I voted lighting, its a pain in the @$$ for me, I cant seem to ever get it the way I want. unless im moveing the bloody light sources all over the scene for 2+ hours. :x