I am running Mandrake 9.2 -amd64 on my amd64 3000 and install was a relative breeze. It was just like any Mandrake install. Even picked out my via sata controller on my K8T800 motherboard as a raid volume too. Sound needed tweaking after install. as there was some static on it.
It installs pretty quick too. Mainly because it seems to lack alot of the extra packages you never use.
Main problem so far is getting my HP psc1205 printer/scanner to work but that is a problem no matter what distro I use. This time I seem to be lacking the sane lib file rpm for hpoj but I am sure I wil get there in the end.
I have used linux and off for a while but I am in no way a guru. So far its the only usable amd64 distro I have found. I just dont have the patience to do a gentoo install