Can someone explain overhead in the DB to me?

I have noticed since upgrading to WP 3.0 that I am getting overhead created in the WP options table in the DB.
I can repair and optimize the table and it goes but even after just a couple of minutes it's back.

Is it something everyone gets or is something causing it which I should try to stop?
Basically does anyone else get it and is it normal when you haven't installed or deleted anything on your site?

Thanks.