i've personally installed a bunch of the latest distros
they have all been buggy on AMD_64. they're getting better, but i don't think it's quite there. i found suse pro the most stable on amd_64.
by all means give it a try if your into tinkering, but a lot of things won't work "out of the box" most notably, browser plugins with a 64bit browser.
the best solution i found is to install an i386 distro, then upgrade/compile the kernel to K7, or even K8/AMD_64.
you'll be using 32bit libs, but the kernel will be optomized for the amd processor.
i haven't been able to tell any differene in speed with a 64bit kernel.
good luck
oh, my favorite site listing distros
http://www.distrowatch.com