The guide also offers a hack that lets you transfer your email from one Gmail account to another Gmail account (it should work for normal Gmail accounts too):
The solution is two-fold. First, in the original Gmail account, make sure you've enabled POP Email in Settings|Forwarding and POP and selected Enable POP for ALL MAIL.
Then, logout, and login to your destination account in Google for Apps and from Add an Email Account, enter in the Gmail username and the POP Server as 188.8.131.52. Also, note the non-standard port 995. Don't select "Leave a copy" because Gmail won't let you anyway. However, don't worry, your emails won't be deleted in the source.
The conclusion is that Google still doesn't offer enough tools to make the migration painless and without buying/using third-party solutions.