Its been what-- 10 years now that we have had 64 bit cpus? Like you said the change from 16 to 32 went by quickly because it was needed and you could see a big difference in performance. With 64 bit, this doesn't seem to be the case that much.
I think Microsoft should have made XP the last windows 32 bit operating system with a c based api. All those years they worked on Vista should have been a new api based on c++ and 64 bit only with no backward compatibility. Just say you like 32 bit and your software, we will support XP for so many more years, lets say a generous 7 years or 10. That gives plenty of time for people to migrate when they could have seen a new Windows 64 with a modern C++ based Api with no legacy support to worry about.
I think mobility is key too John. I have only one desktop from 2005 in my ownership anymore. Everything else is netbooks and notebooks or mobile devices. I love the grab and go ability these products offer with the flexibility to have a nice monitor and keyboard/mouse use when home.