That's a phenomenal adoption rate, and I figure it's entirely driven by cheap memory.
[ Check out Randall Kennedy's "32-bit Windows 7 or 64-bit Windows 7?" in InfoWorld's Test Center blog. ]
Here's how it works: Just a year ago, hardware manufacturers used to design mainstream machines around 2GB. After all, 2GB was -- and still is -- all the memory that most folks need. But with memory prices falling, bumping a system from 2GB up to 4GB right now adds a tiny amount to the build cost of a new PC: less than 5 percent, maybe much less. But to address 4GB you need 64-bit Windows.
The perceived value of 4GB of memory far exceeds the build cost. If you're looking at buying new PCs, and you can get a 4GB machine for 5 percent more than a 2GB machine, you're going to choose the bigger box, right? Even if you don't need the extra memory right now, it's cheap insurance -- and whoever reviews your purchase decision is going to think that you're a shrewd, forward-looking, and insightful shopper. And because 32-bit Windows can't handle 4GB, 64-bit Windows comes along for the ride.
Of course, that's not the way Microsoft spins it. Redmond would like you to drink the marketing Kool-Aid and believe that people install 64-bit Windows because it's better. Brandon let loose with this one: "If you are like me and are running tons of apps, you can see a real difference in performance" -- which should've made his nose grow a couple of inches longer. The simple fact is that 64-bit has become popular because people want 4GB systems.
There's absolutely no doubt that 64-bit Windows has problems, particularly with older peripherals and recalcitrant drivers. Peripheral manufacturers have very little financial incentive to make their older hardware work with 64-bit PCs. I've written here in Tech Watch about problems with the 64-bit version of Microsoft's own Office 2010.