I just setup a framework for myself using an Opengl 3.3 context and rendering CEGUI to it and it works so far.
There is no problem with deprecated functions afaik, as long as you have compatiblity mode activated (default). I don't see why you would want to go for Opengl 3.x core profile. Do you want to?
However, I see no real benefit for CEGUI in using OpenGL 3.x, and as long as you as user of this library do not directly modify with the CEGUI implementations you shouldnt be bothered with the way CEGUI is running, as long as it runs. I guess it would be a lot of work to change all fixed function stuff to utilize shaders and vertex buffer objects instead in CEGUI, and not really worth the effort, as there are more important things to do.
Anyways, I will report on any problems i will (or will not) encounter with CEGUI + OpenGL 3.x here. But I don't expect troubles, that's what the compatibility profile is good for.
EDIT:
I had some problems when using CEGUI with my OpenGL 3.x code, but they were only my fault: If nothing is being rendered after you rendered OpenGL 3 stuff you should get really sure you have unbound ALL buffers and pointers and textures and whatnot. I forgot about my buffers
now it works fine.
