Check mollom (mollom.com) . They have a automated system that scans the comment for spam and if so they present a captcha. There is a free version for up to 100 comments a day.
yep but it doesnt work for all the drupal core+modules mostly needed for field storage like: article-body,comment storage, field storage, sessions, cache, queue (most of the stuff)
More info: http://drupal.org/project/mongodb