What would be the advantage of 128bit. MS has a looooong way to go to even fill the shoes of the 64bit address space. I think 192GB is the high water mark right now - and that is peanuts compared to the open prairie behind it.
Regarding the XP migration, I see some movement. In my Florida computer club (650 members) and a lot of little old ladies, I see more and more interest in Win7.