Mollom is a service that improves the user generated content (UGC) on your site. Although the most common use would be to fight bots flooding your site with spam comments, it does more than that. Dries and Benjamin Schrauwen worked on Mollom, and it will expand beyond Drupal, even into Java web applications.
Read what Dries says about the service on his blog.
I have been running the private beta on five sites for about nine months (uid #11 on mollom.com), including my own as well as a client's site.
I can only say good things about it: it does the job cleanly, and weeds out the garbage content. It is also mostly non-intrusive: it tries to decide whether the node/comment is ham (hello to Jews and Muslims!) or spam based on its heuristics, and degrades to a captcha when it can't decide as a last resort.
It is even good in edge cases: my personal site has a section on email scams (you know the type: African dictator widow wants to give you million, Microsft and Heineken lotteries, ...etc.), and people post comments about scams they got, and it works great.
Here are graphs from two sites, showing interesting things:
Case 1: High volume site, normal usage
The following graph is from a "normal" site. You can see that the ham is green and the bronze is spam. Mollom decides what to do, and it works well. You can see that it did indeed block a lot of garbage content.
Case 2: Less volume, with comment mail
The other graph is from a site that has comment mail installed. In this case, I want to review comments before they are posted in real time, rather than having to go on the site and review them regularly. So Mollom weeds out the garbage, and I am notified of the genuine comments for quick approval.
This is why you will see only the bronze part of the graph.
So, what does Mollom mean? I asked Dries about that, and he said it does not mean anything.
My guess is that he likes the fact that it is a palindrome, and the nice new logo shows it.
Rock on Dries, congratulations and thanks for a great service ...