Quite honestly, this discussion is getting old. First of all, 64-bit is not something new. I was using a 64-bit workstation at the university back in 1995 and then when in 1998 it was up to me what machine to buy for our new project, I went with a 64-bit Dec Alpha. At that time I would not even look at Windows-based PCs.
Now, the current Intel processors are almost all 64-bit. So when I bought my current computer a couple of years ago or so, I went with Vista 64-bit, even though Dell did not officially support it - they did send me a DVD though. Since then I have installed the Windows 7 x64 when it appeared as a beta and then kept upgrading to the newer stable versions.
I have never experienced any problems with it at all. True, I choose 64-bit applications when the choice is available, and sometimes, as was the case with the Sony Picture Motion Browser, I need to download a special patch for the software to work, but basically I've never even saw a program that would not run on my machine. The programs that whs mentioned, I have never used, but then there are millions of apps out there, I'm just saying I manage just fine with those millions that work with x64 OS. And some software that I use is very much professional and specialized. In many cases the authors claim no support for Windows 7 altogether, regardless of flavor - but it all runs just fine.
The only annoying issue is Adobe flash, or the lack thereof for 64-bit systems. Thus I have to keep a copy of 32-bit Firefox for the sole purpose of showing my son cartoons from YouTube. Other than that I use the unofficial 64-bit version and I am very happy with it. It's faster, more stable, and consumes less memory, not that this is really an issue.
So, my experience is, that unless you have some legacy software that you absolutely must run and that would just not run under x64 OS, I see no reason to stay in the 32-bit world.