In My Humble Opinion - The cries about Vista 64 (Vista in general, really) are based mostly on misunderstanding, disinformation and the ever present "Little Chicken Syndrome". Yes, it had some teething problems - (and these are/were nothing compared to XP at release, but that's a longer span of time than the Internet's collective memory, apparently) - and at release there were some key vendors who didn't step up with reliable/working drivers. Top examplese here are that Creative didn't release any that worked for a year, nVidia's drivers could cause problems, and many were just plain inefficient to begin with - causing performance loss. But a year and a half and a service pack later, these have been ironed out to great extent.
A little reality:
If you have very old programs and/or accessories around, you may have problems getting them to work with Vista (whether 32 or 64 is irrelevant here). For new programs/peripherals, to get the Microsoft label, they *must* run on both V32 and V64.
16 bit programs and programs with a 16 bit installer will not run on Vista. Support for 16 bit programming has been removed from the OS. So this is a no-go, unless you have some good virtualization software that can do that for you.
32 bit programs with 32 bit installers WILL run. Occasionally, you may need to specify a compatibility mode (Right click, Properties, etc...).
User Access control is annoying, but can be shut off.
If you like to play with shareware/freeware, Vista 64 requires signed digital certificates and will not allow a program to run without one.
There is still no 64 bit version of Flash Player, but you can run the 32 bit version perfectly well in a 32 bit browser (I use Firefox)
There aren't a lot of native 64 bit applications around. But Vista 64 runs 32 bit apps perfectly well. I have yet to install one that *didn't* work, though like other posters here I don't use old versions/software.
I've been running Vista 64 for close to a year now, and ran Vista 32 before that for a couple months - In my experience, 64 is clearly the more robust operating system. The simple example there being that no application failure has ever taken 64 bit Vista down since I made the change.