Mollom is the new start-up of Dries, Drupal's founder.
It is defined not as a spam-protector, but as a Content Monitoring service. In simple words - when you use Mollom, you permit Mollom to decide for you, whether the content is legible or not.
I just started using it, but I'm quite sure it's the kind of services that you trust, and you don't go and verify every little thing it does and says. Just like Gmail's spam control - sometimes you find an important mail in your spam folder, and you accept it as part of the deal - they block 99% of the spam, and they're allowed to make mistakes.
Since Gmail is such a great service, most of us don't really care that their robots read our mails, in order to offer us some targeted ads. Once Mollom becomes a great service too (and those who used it for a while report it is indeed a good service), it will be as trusted as Google is.
The identity data is stored for two months, after that, the data is stored anonymously for two years.
My guess is that Mollom will become the standard spam fighter in the Drupal community (Acquia will probably use it), and since it's not platform dependent, it might become popular outside Drpual. This will mean that Mollom has the potential to become some sort of a global-moderator, that will decide for us what is ham and what is spam (myself, being Jewish... well... it's kind of the same :-) ).
Now, I'm not an economist, and my visions are usually in the less profitable aspects of life, but I'm sure some of you can come with about 1001 brilliant ways of taking advantage of being the cop in the junction.
So Dries, thanks for letting me know when and where I can buy your shares, I'm sure they'll be pure gold.
oh... and also thank you for blocking spam in my sites from the moment Mollom was installed ;-)