It's hard to say what the hacker's intensions were. They may have done a "test run" on your MobileMe account to see if it was vulnerable perhaps with plans on using it later. That's what happens when using a weak password.

Definitely use strong passwords and buy\use a good password manager to ease the burden of remembering all those passwords we have. The best one in my opinion is 1Password. Here's the download LINK.

They have versions for the Mac, Windows, iPhone.