SLV (Spam Link Verification) is a service run by Russ Jones at www.linksleeve.org. The idea is that interactive sites like Geeklog or forums send all user-contributed posts to SLV first which then checks if certain links show up in unusually high amounts. In which case it considers those to be spam and flags them accordingly.
The SLV module for Geeklog's Spam-X plugin makes use of that service. See the included README for installation instructions.
This module should be considered experimental for now. I've been using an earlier version on two sites for several months now, though, and it did help quite a bit. And it can only get better the more sites use it.
As you probably know, MT-Blacklist has been discontinued quite some time ago and since then Geeklog didn't have access to an up-to-date blacklist. The plan is to remove the MT-Blacklist module from the Geeklog distribution eventually and replace it with something else. And the SLV module is one of the candidates.
So please give this module a try and provide us with some feedback. Thanks.