Any of you probably heard about spam bots, which submit spam to forms on our websites.
Most obvious solution would be to place a captcha on a form. But I don't like captchas because they make entering data on a form a lot harder for me. If I see form with a captcha I'll better go to another website without
captcha and fill out form there.
If you think the same, then reading http://nedbatchelder.com/text/stopbots.html article might become handy. Ned there describes popular techniques to prevent bot submissions.