Online Journalism Review has a good primer on comment spam.

My own struggles with it were frustrating, time consuming, discouraging and I refused to accept this spam as the cost of blogging and doing business online.

Just what the heck is “comment spam” and how did it get so many prominent bloggers up in arms? Basically, spammers have been using blogs to help boost their standings in Google searches by posting massive numbers of comments that include links to their pornography sites, scams and get-rich-quick sites. If your site is linked by a top-ranked site or blog, then Google will often raise your site’s ranking — at least that’s the thinking of spammers.

In fall of 2003, spammers flooded blog comments, using automated schemes to infiltrate comments on high-ranked blogs such as Dan Gillmor’s eJournal, David Weinberger’s Joho the Blog and Rafat Ali’s PaidContent.org, among others. What followed were a series of measures, counter-measures, tactical warfare and the usual gnashing of rhetorical teeth in the blogosphere. All three of these bloggers had to turn off comments for a period of time and are only tentatively trying out new solutions to keep the comments alive.

MT Blacklist couldn’t handle the deluge even though it is recommended that you do not rebuild or add more thatn 25 to the list at one time until the spam is cleared. Try that when there are thousands. It doesn’t work

I used several techniques after consulting with others and it took awhile to find a viable solution for BDBO.

The problem with comments, open forums, e-mail discussion lists and other user-generated online content is that it takes work — usually a moderator or trust system — to make sure the comments stay relevant, clean and spam-free. In fact, spammers have made old Usenet groups unreadable, have flooded most e-mail inboxes, and have brought their multi-level marketing messages to every open chat room, bulletin board and online guest book they can get their digital paws on.

The following are some highlights and lowlights in the War Against Comment Spam, including spammer strategies and blogger counter-strategies; the words of war-mongering bloggers and defeatists who’ve thrown in the towel; and links that can help you win your own personal war with comment spam before you go AWOL from your senses.

Spammers also target trackbacks. I rarely use them, knowing that.

I will not accept spammers taking my bandwidth and my piece of mind.
As technical people continue to work on these problems the article suggests some pratical solutions - for now.

I had FTP codes changes, hosting spam filters tightened, archive comments closed off, MT blacklist updated and used daily. Codes were put in by my tech to stop spammers from sliding through MT holes. I contacted a journalist, and complained politically. I’ve notified two levels of law enforcement, my ISP and my hosting company amd had a friend familar with security attempt to trace the source. If he’d had time to find them I’d have laid charges.
I will probably get hit again. I’ll tighten some of the above procedures.
What I will not do is capitulate to guys getting 1/10 of a cent per link.
My bandwidth is not thiers. Nor in my interaction with readers going to be paralysed or stopped by spammers smart tactics.

Those of us that have been hit by thousands of peices of this automated spam can point each other to workable solutions depending on the platforms we use.