I read here somewhere that there's preliminary support for the AMD Fusion architecture available for the latest Radeon open-source driver. What's the situation with using the older drivers from last quarter's (Oct-Dec 2010), Linux distros such as Ubuntu 10.10? Is it the same with Intel Sandy Bridge, which reportedly will not even boot with the Vesa driver? So what precisely will/won't work with AMD Fusion, with regard to:
(a) booting into a console (I suspect this will at least work)
(b) starting X (with at least the VESA driver)
(c) starting X with the Radeon driver
(d) hardware graphics acceleration (I suspect 3D won't work, what about XVideo and friends?)
2010-Q4? No luck there. 2011-Q4? Depends on the distro, but if the distro cares it should be possible.
The drivers are ready and will do all the things you asked; whether they will be included in your distro of choice may be a question better suited for the respective distro's forum.
Of course you should be able to upgrade an older distro to include all the needed bits for fusion support (upgrade xf86-video-ati, mesa, libdrm, kernel), but whether there are official packages or not depends on the distro.
My understanding is that (a) and (b) should work while (c) and (d) would not. I don't expect that there's been much testing though, since everyone's focus was on getting (c) and (d) working when using newer drivers.