This question is something we've also been asking ourselves on the E3
team,
as part of our work on account creation. I think we all agree that
CAPTCHAs
are at best a necessary evil. They are a compromise we make in our user experience, in order to combat automated attacks.
That's kind of missing the point of the original poster. The point being that they are an *un*nessary evil and do not prevent automated attacks whatsoever.
[Snip]
To get more numbers on how much taking away the CAPTCHA might gain us in terms of human registrations, we have considered a two hour test (to start with) of removing the CAPTCHA from the registration page: https://meta.wikimedia.org/wiki/Research:Account_creation_UX/CAPTCHA That kind of test would probably not be an accurate measurement of what kind of spam would be unleashed if we permanently removed it, but the hourly
volume
of registrations on enwiki is enough to tell us the human impact.
That would be interesting. Remember that captchas arent just on the user reg page though.
-bawolff