I find them to be more trouble than they are worth. While the comment spam filtering technique absolutely rocks in SubText (my blog engine), it isn't very effective against trackbacks and pingbacks. They are all moderated so my site isn't soiled by them, but it is a PITA to approve/reject them. Commonly I find a vast number more trackbacks/pingbacks that are spam than are valid, so I am tossing in the towel. I'd rather make better use of my time than wade through that crap.
Blog post comments will remain on, and moderated.