Blog spamming has no limits... 
As you already know, on my blog I'm using a two-way antispam filter: a CAPTCHA filter to prevent automatic posting and a SQL filter to automatically remove spam comments that could bypass the CAPTCHA (and also a rel=nofollow tag for links on posts).. These 2 ways together works really good, but today I've observed a strange thing: my trackbacks number was growing a lot (about +40 in a day), impossible!
I've decided to check the trackbacks and, after logging to the administration section of my blog, a terrible discover appears on my eyes: lots of trackbacks with a spam url (always the same, poker, casinos etc.). 
Spam bots was blocked to spam via normal posting and they've found a new way to post spam via trackbacks. I've now removed all the references but I've to create a new antispam way I think.
This is an alert for all the blogosphere: check your trackbacks number and check your trackbacks URL to see if they're spam. This is the last way to break our balls!!