If you're running out of space in your Gmail or Google Apps inbox, the quickest fix is nixing the largest attachments you've got stashed. You can't do that from Gmail's web interface - unless you've enlisted Find Big Mail's help.
Once it completed scanning my account, I simply clicked the label that said FindBigMail > 2mb, selected all messages, and clicked Delete. I then went to the trash folder and emptied that. Voilà - I dropped from 64 percent occupied space to 36 percent. How awesome is that?