I use Gmail and keep everything in the cloud. I got tired of using a different computer to check mail and not having something I was looking for because it was in an Outlook .pst file on my computer at home.

As far as the security concerns raised above go, I guess I'm just not important enough to think people would want to snoop through my mail. If there were anything I really wanted kept super-private, I would either communicate it in person or use PGP.