The FAQ has an entry in the table: RV670 Radeon HD 3000 series none, support is in progress It also has a note afterwards. It would be nice to note that support exists with the xorg driver that's currently in ~arch, xf86-video-ati-6.9.0. I'm not sure of the status of support from the binary drivers.
Also, the R500 and R600 entries are supported in 6.9.
Thanks for reporting! Fixed in CVS. commit log: add info for bug 230911. also, i did some more digging on binary and xorg driver support, and have added some free additional bonus information, and some info on the 4000 series, which is soon to have support in xf86-video-ati, probably into the next 6.9.x update, or whatever comes next. just a matter of PCI IDs and such; see phoronix.com for more info on that.