There still are various apps and things that don't work under x64. To list a few that I've been struggling with this past few weeks,
- MSI Live Update, so no BIOS updating through Windows. You've got to find a floppy drive and disk from somewhere instead. Ick.
- RUU update utility for WinMo phones doesn't work under 7x64. As I recall, neither does the Nokia firmware updater.
- Tridef's game 3D anaglyph'ing software
There might've been other stuff too that I've forgotten about. It's not always a major issue though, since VMWare is happy to run an x86 WinXP instance that can interface semi-directly with USB hardware and update phones and whatever else, and none of these issues are exactly major show-stoppers.
Agent put it well when he made the point that the question is more of "Why should I go 32bit?". 2GB PC6400 assembled by PNY costs £18 over at Play.com. I have 8GB of it in my system because, well, why not? 5GB extra RAM for £36. My mate spent more than that on his haircut the other day. Difference is, I don;t have to lie to say that having an extra 5GB of RAM is great.