When I tried to upgrade to 2005.0 profile, as one of the trailblazing testers, I failed. Also, in trying to salvage the half-operational consequences, I broke my binary utilities. That means the assembler, the linking loader, and stuff like that. When I compile new stuff I have it make a binary package at the same time, so I simply re-installed from the binary package. Then I tried to go back to the 2004.3 profile and start again, using the lessons that testing had given everyone, but I had broken my compiler, and restoring from binaries did not fix it. Eventually I fixed the compiler via a great deal of magic and hocus-pocus, and went back to 2004.3 profile. By this time the Gentoo amd64 developers had figured out a reliable routine, which I undertook, and now I'm running 2005.0 profile and am a happy nerd.
You still can't run DOSEMU with a 64-bit kernel, however. Dang.