I think the whole 64-bit RAM thing is overblown. Unless you're already maxing out RAM or near it, I wouldn't worry about it. Running 64-bit Kubuntu (not an efficient distro or DE) with Kwin effects, Firefox, Tbird, and Synaptic open, I'm only using 800MB. It's much less on my main install (Debian sid/xfce). That said, I don't think I'd reinstall just to move to 64-bit unless I was doing something that really benefitted from it (running VM's, lots of encoding, big GIMP images, etc.).