Tried it, like it. Worried about how easy it is to create a site without any 'are you human' checks though. Isn't this going to create tonnes of bot sites?
This was a worry to us. It'd be a big detriment to us if that happened. We're trying to keep the user the priority, rather than nasty captchas. So we've got our own implementations. The moment we see bots, we'll switch our strategy. :)