The latest kernel, which i'm posting here as amd_kernel, was built by Andy Vandjick, but that wouldn't be possible without the amazing work by Sinetek (who made the first ssse3 emulator ever, enabling non FX-series CPUs to run OSX in 64-bit kernel mode), R:A:W:x86, Bronzovka (who made Lion on AMD possible) and the Voodoo team. Many thanks to them all!
The correct boot flags to run the kernel are amd_kernel arch=x86_64. FX-series users must also add the correct busratio. The kernel is not working properly with nVidia graphics (and some ATI ones), so their users must also either add -x (safe mode) boot flag or disable GeforceGA.plugin and GLDriver.bundle in System/Library/Extensions.
FX users may also try the 12.0 AMD kernel by sinetek, which is confirmed to be working nicely with newer AMD CPUs (Bulldozer and Piledriver chips). Bad news are that, since it's a 12.0 (10.8.0) kernel, it won't work with 10.8.2 without mods; specifically, it's necessary replacing the 10.8.2 AppleFileSystemDriver.kext, IOACPIFamily.kext and perhaps AppleACPIPlatform.kext by the 10.8.0 versions of each one.
Good luck to all and please post feedback. The sources are also included for anyone wanting to build the kernel from the sources, or help improve it - there's still a lot of work to do.