I have been running Mollom as my spam-fighter on this site for not quite two months now. It's been fairly effective overall. The nifty flash meter shows me just how bad the spam problem is (good grief, 593 blocked spam messages just on 15 May!), and I haven't gotten any spam in my comment list yet.
That is, until today, when a new form appeared.
You won't see them, because I already deleted them. However, earlier today I noticed a few comments that didn't quite make sense in context. They were on blog posts that were already several months old (not itself unusual). They were well-written, on-topic, and had no links in them. But they seemed, well, familiar.
They were, in fact, duplicates of previous comments on the same story; in one case, it was the first paragraph of the blog post on which it was submitted. So I checked the home page link for the submitter. It wasn't your typical spam site, at least I don't think so, but it did look, well, overly commercial. Lots of banner ads (no porn, fortunately), links to some sort of YouTube service... Hm. Still, they added nothing of value so I simply canned them.
Is this the next form of comment spam? Filtering that, even with a system like Mollom that supports a "sausage" status for questionable content, will be quite difficult even if it's possible. Perhaps it's time for a reputation system? Hmmm...