I don't expect Athlon 64 to be a big seller just yet, for the simple reason that Windows64 isn't expected until 1Q2004. MS released a public beta today, to go with the launch of the chip, but I doubt PC makers are going to sell systems with that. Of course, the chip runs Win32 just fine as well, since it is an x86 part, but the real performance increases come with a 64-bit OS, and then 64-bit applications. But you can get Linux for AMD64 today - of course.
I expect the next system I buy will be an Athlon 64.