Turned off comments today. The WordPress built-in checks for too many links in one comment, or certain common "spam" words worked well for a while. More recently Kitten's Spaminator did an excellent job of suppressing the last wave of automated comment spammers.
Today a couple comments appeared with one link per comment, and none of the common spam words. I don't want to make a hobby of cleaning up after spammers, so comments are off.
Seems that with "trackback" there is a lot less need for comments. On the other hand, I do not know if trackback (either outgoing or incoming) works with my WordPress installation.