I hate to say it, but I think this is a huge step in the wrong direction. First, there appear to be multiple correct answers for almost all the challenges. One showed a picture of a woman watering plants that appeared to have dollar bills as leaves. It asked me what she was doing. I had no clue what to put; is she "watering plants," "growing money," or just "watering?". I think you should at least provide multiple choice answers, even if the user has to enter in the full answer word for word. Forget about spam bots being able to figure these out, most humans would have a hard time!

Second, and this is a big one, I don't think there are many bloggers and web developers out there who are so frustrated with captchas that they'd be willing to use an ad-supported system, no matter how easy it makes things for the end user. I know I wouldn't. The ads also add a lot of confusion to the captcha. Again, on the money plant watering example, I saw an ad about making cash online. Combined with the strange money tree it made for a very confusing experience at best. I think having the same crap that spambots are likely to post on a site as advertisements on the very captcha that is trying to prevent it sends some pretty mixed signals.

Third, why does this need to be crowd-sourced? This seems like it's adding myriad quality control issues. I think if you sat down and came up with 10 or so internationally universal puzzles that are easily solved by all humans and not by robots, you would have enough variety to keep the bots guessing.

What I want to see is a captcha that determines I'm human without me having to do anything. I don't even know if this can be done, but to me all captcha solutions should be aiming toward that goal. In the meantime, I'll deal with the captchas that are out there right now.