Is nicely explained by the Lifehacker crew. It’s not the exact setup I use, but the main point is the same.

Upon reflection, one of the fascinating consequences of GMail using IMAP (which, by the way, is a very significant technical achievement, as IMAP, while a very powerful protocol, is also very hard to implement in a scalable way) is that people can now get free email with an IMAP server. This is important not just for power-users like the Lifehackers, but also for people using smartphones (iPhone, Treos, etc.). I wouldn’t be surprised to see the other major webmail providers coming out with IMAP support as well. We may see yet see IMAP get its fair market share.

For many, IMAP support turns GMail into a high-performance mail server with spam filtering, which by the way can be used with a web front-end — as opposed to what it was last week: a webmail system with POP access.

This email world is a lot more fluid than people realize.