I am seriously considering moving all my e-mail -- including years of archives currently stored in my laptop and managed by Thunderbird -- to Gmail and, from then on, using IMAP to access it.
Right now I POP all my e-mail to my laptop. In the new setup, I'll POP all my e-mail to Gmail and will then use either its web or IMAP interface (via Thunderbird) to access all my mail. [I wrote about this in a lot more detail on my personal blog.]
I like the idea of cloud computing and the ability to access my calendar and all of my e-mail regardless of where I am and what e-mail client, browser, or mobile phone device I'm using. Of course, actually doing this will take a lot of time since I have over 2GB of e-mail archives to upload...but I suppose it'll be worth it in the end.
Here's hoping everything goes well (as it is so far).