How about this? ReCAPTCHA is very annoying. Even though it scans books.
Although none are perfect, at least reCAPTCHA has some accessibility provision. (It's text-only so doesn't require dexterity to use, plus there is an audio option too). You need to provide the most number of users with the ability to use the site, inaccessible CAPTCHAs reduce the number of users.
Also, at least reCAPTCHA gives something back to the web - for those that don't know each time a reCAPTCHA is entered it helps to digitise versions of books that otherwise would remain print-only. (Source: http://www.google.com/recaptcha)
I don't know how to make pancakes:
I don't want to catch little beautiful butterflies either:
Google reCAPTCHA is far better than this since it has a typing facility which is faster than by mouse. I don't use the mouse to submit a post; I just press enter and if the CAPTCHA appears, I just want to type instead moving my hand and using the mouse and thinking how to make pancakes.
I think both CAPTCHAs have their problems:
reCAPTCHA can be down-right impossible to read sometimes.
reCAPTCHA may require you to type characters that aren't even on your keyboard.
reCAPTCHA can't be used in countries that block Google.
PlayThru might be cumbersome for somebody that isn't skilled with the mouse or has to use some poor mouse replacement.
PlayThru assumes you're familiar with things you may have never seen in your life.
The free version of PlayThru requires you to understand English. All versions require you to be able to read.1
Personally, I think PlayThru should be easier to solve than reCAPTCHA nine times out of ten, but most of reCAPTCHA's problems can be solved by refreshing repeatedly.
So why use only one? Let's display both CAPTCHAs, but require the user to solve only one. This way, everybody's happy.
1 For Stack Overflow, that may not be a bad thing.