For those looking for a Drupal CAPTCHA product or service, I still remain very happy with the Mollom CAPTCHA service. Like Drupal, Mollom was also created by Dries Buytaert, so as you can imagine, it integrates very well with Drupal.
Here are some more details on my Mollom Drupal CAPTCHA experiences to date.
As mentioned in my Mollom CAPTCHA service review, Mollom installs into Drupal just like any other Drupal module. Just download the Mollom client, and install it like you would any other Drupal module. Then, set up a Mollom account, get your public and private keys, configure which web forms you want to protect (i.e., the Drupal comment form, contact form, etc), and how you want to protect them (text analysis, CAPTCHA, or a combination of the two), and you're in the CAPTCHA business.
Drupal CAPTCHA with Mollom - over three weeks so far
Now over three weeks into using Mollom on this website, I'm very pleased with how it's functioning as a Drupal CAPTCHA service. I just checked my Mollom statistics again, and Mollom is eliminating 20 or more spam attempts every day on this web site, including spam attempts against the comment form and contact form that I never even see or have to deal with. At the same time, it's letting the legitimate ham attempts get through, which is a good thing.
I'm very happy with Mollom as a Drupal CAPTCHA service, and I'd like to write more about it here, but hopefully I covered it pretty well in my Mollom review, so I'll leave it at that.
If you have any comments or questions about Drupal or Mollom, just post a comment below, and I'll be glad to share anything else I know about these two products.