A week ago George Ou made a very good post which took an objective look at choosing between x86 32-bit edition or x64 64-bit edition of Windows Vista. It's a good post and if you've not read it yet, I encourage you to do so. But there's one point that George didn't consider - why aren't computer users who could run a 64-bit OS (that is, they have drivers for everything in place already) not already doing so?
I think that the reason can be summed up by two words - why bother.
Seriously, while there might be advantages to making the leap from a x86 32-bit operating system to an x64 64-bit OS for servers or certain specialized workstations, for the average desktop user, there's little or no advantage. Sure, you can boost the amount of RAM that you can utilize from 4GB all the way up to 128GB, but how many desktop or notebook users need more than 4GB of RAM?
On a side note, I'd suggest that for best performance that you double the amount of RAM that you fit into a system that's going to run a 64-bit OS, so if you're been used to running Vista 32-bit with 1GB of RAM, boost that to 2GB when running a 64-bit OS.
Nope, while the 64-bit road is open to all that have the right hardware (and compatible drivers), but there's little in the way of incentive to take it. While all your existing hardware might be compatible, you never know when you're going to pick up a scanner or printer that's not compatible, and then you have some serious headaches.
But (there's always a but), even if you're not planning on making the jump to 64-bit right now, it's time to start planning for the future. There's already a good chance that the next version of Windows (Vienna, Windows 7, whatever you want to call it) will ship as 64-bit only so slowly eliminating hardware that doesn't have 64-bit drivers might be a good idea (although if take-up of 64-bit Vista remains low, and hardware manufacturers continue to ignore x64, Vienna might also come in 32- and 64-bit flavors after all).
Oh, and it's also worth bearing in mind that this isn't something that only Windows users need to think about. 64-bit Linux distros are widespread. The 64-bit desktop PC is certainly coming, it's just hard to know when.
Thoughts? Are you already using a 64-bit OS on desktop systems? Do you have any plans to make the switch? Are you eliminating hardware that has 32-bit only drivers in preparation for future migration?