Here's what I've done with gmail, what's happened and what I think about it after a couple weeks of light use:
Received 3 free invitations to send out. I've got one left and am open to requests from regular readers and/or bloggers.
Created an Apple Mail rule that made every email I receive at my regular inbox redirect to gmail so a copy of current emails goes there. Unfortunately, the spam goes there too. I'll let you know how well the spam filter works in my next update.
Deactivated all my other mail rules and then applied my redirect to gmail rule to my entire 1000+ sent mail folder. It took 5 hours - pretty slow and finally crashed Safari. I haven't yet determined whether all of my sent mail made it over yet but it seemed to work just fine until it crashed. Speed seems kind of like running an Applescript only slower.
Created about 20 labels to apply. Have been labeling all the Sent mail I redirected as *Sent* and then archiving it. Probably unnecessary as filtering for my name in the From field works well too.
Gmail has behaved badly quite frequently. When I do a lot of labeling and archiving - say 5 - 10 times - somewhere in there I get a Safari crash. So, Safari works now but it's not close to 100% reliable yet.