However, my main PC at home utilizes a 64-bit version of Ubuntu 7.04 Feisty Fawn, and Virtualbox didn't support 64-bit OSes — until this month. Now that I've tried it, I'm happy to report it works just as well as its 32-bit sibling.
Read it at Linux.com
Other than a few minor annoyances, everything else worked fine with each OS. Browsing the Internet, checking email, and playing games without 3-D acceleration worked as expected. Each OS ran just about as fast as it would if installed on a physical PC.
Virtualbox is amazing. It may not have as many features as solutions such as VMware, but it doesn't have the high price tag either. If all you're looking for is a personal virtualization application with a basic feature set, Virtualbox is useful.