 Microsoft: Adoption of 64-bit Windows Vista increasing
Of course, it's hard to tell what's "popularity" and what's retailers simply stocking and advertising the 64-bit version more than the 32-bit version (I've noticed our local Fry's ads, for example, all seem to feature 64-bit Vista in the desktops and laptops).
But there are some definite benefits to the extra bits, mostly the ability to use more than four gigabytes of RAM.
And it's nice to see that Microsoft is requiring any hardware or software companies that want to advertise their products as "Vista certified" have to be compatible with both the 32-bit and 64-bit versions of the OS. | 
