I had to migrate around 100 accounts out of Gmail (free) in 2009 and it was a pain because their IMAP implementation was sub-par and so all the IMAP migration tools (imapcopy etc..) failed/halted somewhere during the process on each mailbox. At the end we had to configure accounts on various computers and manually download them (probably two bad IMAP implementation, Gmail and Outlook, worked better together than using other tools :)) Of course POP was not acceptable because of lack of labels/folders support.

If this existed at that time it would have saved us a lot of hassle...