As I've noticed a permanent increase in the spam that has gotten through NoSpamNX in the last few months, I'd like to bring up again the idea of adding a timestamp check to NoSpamNX.
I suspect the reason for increased spam that gets through NoSpamNX is that spammers (or the tools they use) have learned to not fill in the do-not-fill field NoSpamNX and other anti-spam solutions use. It's time to add a new trick into NoSpamNX's arsenal: timestamp checking.
The idea is simple and effectively used for example in Drupal's Honeypot module (http://www.midwesternmac.com/blogs/jeff-geerling/introducing-honeypot-form-spam). The module tracks the time difference between when a certain comment form was sent to user and when the user returned it. If the time difference is less than the set interval, eg. 5 seconds, the comment is blocked, since a human would take more than 5 seconds to fill in the form.
These can be implemented via JS or PHP in many different ways.