GTG,
If you subscribe to Gmail, and all the apps that come along with it you'd see why. There are so many benefits to doing so: the ability to check ALL my email from any browser anywhere, not having to sync my mail settings, calendar, contacts, tasks, appointments between multiple computers, not to mention all the aforementioned items can be used universally (on either a pc or a mac).
One of the major benefits is that I am constantly upgrading and replacing hardware every few years. Using googles apps keeps me from having the annoyance of transfering all my data into a new computer... it's simply very beneficial in a long term view... I'm sick of losing mail, contacts and all the turmoil that is part of buying a new upgrade... I plan on using google for the foreseeable future. You really should check it out...
EDIT: I've done some research and there isn't CURRENTLY a way to import mail (that I'm aware of). However, google does list it as a feature that is "COMING SOON."