I thought it was working well. The number of spam that was getting through to moderation dropped to near nothing. No false positives at all (when I bothered to check, honestly).
Now I know how well it was working. The current version doesn’t work with the 3.3 beta, so I disabled it.
Ugh, 20 junk comments a day that are passing through to my inbox for moderation. Sames ones over and over until I go into Spam Lookup and do something so the junk is caught. Until the next new thread comes along. Both spam filters work well on spam it already knows about. Big difference: Akismet learns from its mistakes, Spam Lookup does not.
However, having to go into the “comments” page to manage the junk did alert me to the fact that I missed authorizing two legitimate comments in the last month. Sorry about that! One of these days I should consider going to one of those CAPTCHA systems so the system can evaluate spam on the spot and I don’t have to moderate. Folks just aren’t adopting/using TypeKey that much.