It'd be great to see the Linux version of the Heaven benchmark any time soon. Hopefully with the release of the Nvidia Fermi cards because ATI probably won't have their drivers ready in the first half of this year.
most of the functionality will have already been present in the nvidia and AMD drivers, just in the form of extensions. Not all of it of course, and actually AMD exposed some of the functionality ahead of nvidia.
It's not likely that that the cat 10.3's will have opengl 3.3 (the windows 10.3a driver apparently doesn't), but that doesn't stop people from loading extensions.
Do you want to place a bet who will release the first OpenGL 4 driver? My guess is this month at max next month with a preview driver from nvidia. Hardware will be out in a week too, just you need enough money, gtx 470/480 will be not cheap, that's clear.
Does the ATI 5000 series cards even have all the bells and whistles to support OGL4? Maybe we have to wait till N.Islands (R900).
I think only some of the 5xxx series can offer official hardware opengl 4.0 support. The lower end cards are missing the 64bit floating point support (I read that from the opengl forums anyway).
In either case, it should still be fine to use a kind of wrapper to load opengl3.3, and then required extensions to get almost-4.0 support (if you don't need the double-precision floats). The function pointers will all be the same anyway.