> For some reason I find it satisfying to "pull a fast one" on any captcha service.

Why? What do you achieve except being told you're wrong every once in a while? I mean, you're trying to bother a machine. Isn't that a bit like a reverse Turing test?

I suspect the amount of noise that ReCAPTCHA filters out from automatic attempts is several orders of magnitude larger than anything any group of actual humans can generate.