I was working on our WordPress database looking for an error in one of the posts. While using a PHP based SQL editor I discovered that every post had about 6 or more copies of itself. They were all the previous revisions of that post. Then I realized that records of revisions is why our SQL database is so big!
So then I looked for a way to clean up that huge database. I came across a plug-in called 'WP-Cleanup' and it worked great! It easily reduced the database size from 19.4 megs down to only 3.4 Megs! I would highly recommend WP_Cleanup for anyone using WordPress. It should be run once a month not once a year.
Now I am looking for a way to get rid of all of the unused pictures, there must be thousands of them!