This has been a little weird, but I've recently had to play with browser-based email because my PowerBook died. Also, the Bigfoot mail server that I'd used since 1996 also tanked, which inspired a migration to Gmail. So while my little aluminum baby was away at Apple (you DO have AppleCare, don't you?), I actually moved away from Apple Mail, and I'm stunned how easy it was.
One thing I found, however, was that Safari didn't work so hot with the Gmail interface, so I use the free Camino, which is based on Firefox but made for the Mac.
If you have a yahoo.com address, you might try the Yahoo! Mail Beta in Camino and see how you like it. And check out Plaxo to sync your Yahoo! contacts with Apple's Address Book. (Plaxo doesn't sync yet with Gmail. Check my recent article in the San Antonio Current for some of my thoughts on that matter.