A user-friendly alternative to CAPTCHA
Spam is the job of a business and it's webmaster to deal with, not the user filling in the form. When it is passed on to the user, normally in the form of am image captcha, it significantly worsens the end experience by frustrating the user and making them less likely to complete your form.
The silly thing is that dealing with spam on small-medium sized sites can be very straightforward. One of the biggest worries in detecting spam is the risk of a false positive, flagging a legitimate message as spam just because the user included a few links or wrote it in an unusual way. At the other end of the problem too many false negatives make the process of filtering spam pointless.
The Honeypot is a very easy way to eliminate a very high proportion of spam messages on things like contact forms while be 100% sure you are not going to get any false positives.
Of course this test could be easily spotted by the programmer behind the spambot but for small to medium sites this is unlikely to ever happen. Of course spambots targeting specific websites can be programmed to be much smarter and so captchas are necessary on bigger sites, or in applications where the consequences of letting through someone who is a bot are higher.
In my experience these methods are very effective at curbing the vast majority of spam, enough to allow the intended recipient or system to receive all messages that pass it. Of course, you sometimes have to validate human created content but that is a whole different article.