My Gmail had grown slowly to 55% of 7493 MB overtime. Not a real big concern, but since I was cleaning my Mac I thought I should clean my Gmail as well. A quick google got me to the creativebits site and after reading the article I got a bit depressed. One of the comments from energio though cleared everything up. In your webbrowser, go to Gmail.com, and do a search for:
 
 

• has:attachment (*.ppt || *.pptx || *.pptm || *.pot || *.potx || *.potm || *.pps || *.ppt ||)
• has:attachment (*.mov || *.wmv || *.wm)

This will find all mail including large attachments like movies and powerpoint presentations (you can of course come up with you own line or combine these two or whatever..). After Gmail found these emails you start selecting the mails you want to trash. Don’t forget to empty your trash to see actual result of you action.

With a quick search ‘n trash I earned 18% back of my Gmail cappacity.