This could make things a little easier than dragging folder by folder between two IMAP servers using Thunderbird. Ahhhh. Good times. Good times.
A few months ago, we added the ability to import your old mail and contacts to Gmail. We made this feature available for all newly-created Gmail accounts first, since people new to Gmail benefit most from being able to move their stuff with them. Friends who wanted to use Gmail but kept telling us how painful it would be finally made the switch!