Idea is good for massive/popular spam bots. But... well... I've been there and I know, that spam bots evolve if only there is someone, who can tune bot a little. So changing bot from looking for submit button into just submiting form is quite easy. Also - technology goes forward and there's no big problem today to write bot, that understand JavaScript. And as I have mentioned this - the best solution, I've found to fight spam bots is to create hidden (or visible, what the hell) field with initial value, that's later changed by JavaScript. Checking for value, you expect it to be set by bot works like a charm. But - as long as you say, that this solution works, it's worth mentioning and remembering.