At the suggestion of a couple of sites, including 6A, I installed over the weekend Brad Choate’s MT-DSBL plug-in, which attempts to use open proxy information from DSBL to identify potential comment spammers.
So far, though, the only folks blocked were Randy and Mary, two people I’m pretty certain are not spammers (and who, presumably, are using respectable ISPs). Their comments dropped into moderation (and were posted this morning), but unlike MTBL, I had to actually view the Comments queue to spot them.
We’ll see how it works over the next week or so, but my inclination is at this point to drop MT-DSBL.
You may want to take a look at http://www.kahunaburger.com/blog/archives/000192.html