From now on, all trackbacks to this blog are moderated thanks to the moderate-trackbacks plugins. Spammers have really a lot of time to waste. Good thing the wordpress community is very strong and fighting back.
Now, the simplest thing is: do not to use trackback. It is a weak protocol (in a spam infested world) and I’ll probably not moderate these very often especially if the queue gets very long. Ping my blog instead (pingback specs make spamming difficult).
Update: Downes has a recent post on a related topic: Trackback is Dead, Use PubSub (though I published this post before he published his!).
Update 2: about 2 hours after installing the plugin, I’ve got 18 trackback deleted. This is 9 spams an hour. And I’m a low traffice web site…