Two days ago I visited 500 wikis. I chose to register on about 40 of them I was interested in, and 20 out of 40 had registration closed because they had been unable to stop spam (one required authorisation of new accounts and another used Extension:ConfirmAccount). As for the other 20, which managed to keep editing open, none was using FancyCaptcha, SimpleCaptcha or MathCaptcha; one or two used Asirra, something like three reCAPTCHA, two used what seemed QuestyCaptcha but with math questions in blurred images, and several were using QuestyCaptcha, with questions tightly adapted to their audience, not always obvious (and impossible for me in the case of SpongeBob questions in German). Edit: sorry, now that I think of it there was one wiki using what looked like FancyCaptcha, but they had such distorted images that it was very hard; I've not checked in their recent changes if this configuration was effective.
