I would like this too.
I noticed because I've had some trackbacks that just reference my site - not a post, the blog as a whole - and they are getting tagged onto the first post I made using WP.
Comments are shut off with the 'auto-close' plugin, but obviously tbs and pings are being added.
If a trackback to my site works, then a spammers job just got a whole lot easier didn't it ?
I've had no trackback spam, but this seems like a great big hole somewhere, and it could do with closing.