This plugin has a GREAT potential!

Seems to be very effective,
I tried it on several sites, and there were a few times that it could not block spam although I used the filters correctly, but it still blocks about 85-90% of spam which is very nice!
I hope that the developer of this plugin will keep updating it and fix bugs, as this plugin clearly has a great potential to be one of the most popular plugins on WordPress, not less than that!