Mike, here are answers:
a) To be honest, this is not my primary anti-spam tool right now (I use mod_security, but that is a separate topic). That said, this plugin is still enabled in my MT 3.33 installation and still catches spam. So it does work, and I am not aware of any incompatibilities.
b) Don't worry about that one. This plugin doesn't implement all of the Blacklist feature, it merely scans each comment / trackback against the content of the blacklist. It doesn't implement any of the link counting features -- you can use SpamLookup for that if you want.
c) Probably your server, but I could have done a better job coding that part so that it works no matter what
d) No. Since this plugin hooks into MT's junk filters, you can't tell it to delete completely. There are a few reason you want them to go to the junk folder. Number one is that sometimes a valid comment gets junked -- if it was deleted, you would never know, and you wouldn't be able to publish it.
e) First, different guys made MT-Blacklist and Spamlookup. Second, spamlookup does actually suck -- it is actually quite capable. The difference between the two approaches is that MT-B included a master blacklist that was continually be updated -- whereas SpamLookup doesn't have this. SpamLookup ships with a blank filter list. Because of this, out of the box, it isn't very effective. But if you added a long list of words and patterns to block, it can be just as effective as MT-B. Most people don't have the knowledge or the time to compile such a list, so in practical use, spamlookup ends up being ineffective.