I ran some very basic opengl tests and compared windows vs linux performance on my hd4850.
The tests can be found here: http://www.songho.ca/opengl/gl_pbo.html , I ran pboUnpack, pboPack, vbo and fbo.
Looks like ati also hasn't implementet PBOs on windows. The factor 10 difference w/o could explain the very bad ut2004 performance I get on linux, dunno if it uses PBOs very much, but it's at least factor 3 slower.
Looks like the pboPack issue was fixed with 8.12. Now delivers 19.8/21.6 wo/with PBO.
pboUnpack also increased, now I get 280MB/s with PBO mode 1 and 2. The other tests increased about 10%, dunno if it's the new driver or my new kernel.