As if you need another reason to install ReverseDOS.  I installed it on June 28th and have not received one referral or trackback spam..not one!  Here is another reason I found when checking on my database backups today, the database size shrunk from 24MB to 6.5MB.  That is 1/4 of the size.  So if you get heavy traffic that can be a lot.

I will say that I did go in and delete all of the referral spam from the blog_content and blog_referrals tables prior to the install so I'm not saying installing ReverseDOS alone will cause your database size to get smaller...but installing it will help keep it from growing faster than it should.