Actually, There are very few native 64 applications, Such as Crysis and video encoding etc..
It's also quite commonly recommended that unless you have 4gb+ of ram, It's probably not such a good idea.
I personally have a 64bit Installation of Linux with 2gb of ram and everything works fine, It's a little bit faster... Haven't noticed anything different in terms of incompatibility from 32 bit to 64 bit.
In the future though 64bit will become standard.. I wouldn't so much worry about getting a 64 or 32 bit with windows 7, Though I think next version of windows it will be a good idea to go 64 bit, At least thats what I'm gonna do.
As more applications become 64bit Native you'll see more benefits.