I've got Business 64bit, now that I think about it, maybe that's why I didn't notice a big performance hit.
Well, there aren't as many drivers for 64bit as there are for 32bit, wasn't a big problem for me, NVidia etc should have 64bit Vista drivers so if your PC is somewhat new, the drivers shouldn't be a problem, unless you have some old digicam or so where there is no real driver support anymore and Microsoft didn't include a driver in Vista.
Also note how you will have a program files (x86) next to the normal program files folder, I don't know whether it's important for Vista(guess not) but it splits up 64bit and 32bit applications this way. There are also two different versions of IE and WMP in 32bit and 64bit. I use WMP in 64bit as it seems faster, IE(if I ever use it anyway) in 32 as Adobe's flash wasn't 64bit compatible last time I tried, maybe they fixed that already though.

Apart from that, the only 64bit related problem I remember was that I had to download a Tages driver for Gothic 3 manually as the one on the DVD isn't 64 bit compatible but that was a matter of a really small download and installation.

That's about all I can come up with now, I think it's about time we move on to 64bit, Nintendo did it years ago.