Google Chrome supports multiple profiles. The feature is just hidden until it is ready for prime-time. It is really easy to set up on the Linux and Windows version of Chrome. On the Mac it takes some manual work.
I'm sure eventually the Mac version will have a nice GUI to set this up for you. In the meanwhile, I've written a script that does it:
chrome-with-profile-1.0.tar.gz
Tom
How do I run the .sh script?