Ink: 16GB may seem like a lot now... but in 5 years? I'll probably still be using this version of Win7 then, so I went with the next version up. I do video editing on and off and graphics stuff, I've been known to play in 3D animation/rendering, so that RAM will eventually make its way into my system. Also, when using 64-bit systems, if I recall, the minimum amount of memory is larger for any given program. Because it is 64-bit programs use more, or some such oddity (?).
Also, I believe that the RAM limit on 32-bit also included the video RAM as well.... So if you had a 1GB or 2GB video card, look out! You might find yourself recognizing only 2 GB or something.
I've got 6GB now and a 2GB video card, I've set the system up with a fresh install (win7 64). I still haven't started installing things other than to test a game or two (checkin' out the frame rates, natch). I don't know if I like the default looks but I'll figure something out. Now I just need to read up on all the services and see what I can lose and what I can keep.