Ultimately, Windows 7 RC is still a beta: no telling what issues are still there, and there are some people who've experienced issues finding the right drivers to make their hardware work under the OS.
On the other hand, based on my experience, Windows 7 has performed well as my laptop's primary OS. I'm still keeping my XP installation though, even it takes up space, just in case something goes wrong with 7 and I don't have the time to immediately troubleshoot.
As for 64-bit OSes, it really depends on what machine you use. Personally though, I would only use a 64-bit OS if my computer had more than 2GB of RAM—which is neither the case with my laptop or desktop.