Very nice read, although I think I will be going 64-bit for one main reason. Price. 64-bit athlon chips are just as cheap as the (almost) equivalent 32-bit processers, but the 64-bits run even the 32-bit code faster.
in my personal opinion, after seeing first hand some of the 64-bit amd chips run go ahead and buy a 64-bit machine if you are in the market right now, but don't think you need to immediatley upgrade your "outdated" 32-bit processor.
I didn't know the Itanium and the A64 were so different
that part was especially interesting.