Honestly, I could spend hours trying to stop the particular people from spamming, but it makes Mike feel really special, so once in a while we need to throw him a bone!
Seriously though, the spam attacks do not happen often and they are being handled very quickly, so it is hard to justify adding more checks and slow downs for a once a week attack.
We can turn off the ability for new members to post without having their posts "validated" by an admin, however new visitors to the board get discouraged if they have to wait a day to be approved as a real member.
If the attacks continue and we cannot keep up, we can turn on other security measures, but it slows down the site and we want to keep it running nice.
vBulletin is a great product, and has a suite of really good counter measures, mobile platforms and blogging capabilities, and we are so close to being able to buy the complete suite. We save a lot of money if we buy the whole thing at once, opposed to the core, then the rest later, that is why we are still waiting on a few more donations ...
Derek