I have reduced the number of splog attacks on my site
I use the Akismet and WP-DenyHost anti-spam plugins for WordPress. Akismet is a must-have and has, since I installed it, caught 304,056 spams (!!). When Akismet catch a spammer, it logs the spammers IP address. WP-DenyHost, written by me, prevents spammers from getting access to my site a second time by blocking access from this IP address.
I installed WP-DenyHost in the fall 2009 and, as you can see from the graph above, the number of spam has dropped dramatically.