On 19/04/2008, Tim Hall wrote:

But I know a lot of other sites don't even if the software supports them; Pingbacks have been badly abused by comment spammers in the past, to the extent that a lot of Moveable Type users have disabled pingbacks because it wasn't worth the hassle.

Wordpress' Akismet spam filter does an excellent job of ignoring bad pingbacks and trackbacks. Also there are number of Wordpress plugins to handle this too. I rarely have a problem with bad pingbacks tbh (but comment spam is a bloom'in pain)