Most UX people can’t stand CAPTCHAs (I could probably say ‘all’, but there is most likely one out there that would make me a liar). For me at least a CAPTCHA says, “I can’t be bothered to try and work out who’s a spammer, so I’ll just assume all my users are spammers and make them prove they’re not”. That’s a terrible attitude.
I’ve found a lot of anecdotal evidence, but here’s an informal study that shows some numbers. This study looked at conversion rates for sites over a 6 month period – 3 months with CAPTCHAs on, and 3 with it off.
The results? It did reduce spam by 88% (91 conversions to 11), ok that’s reasonable, but it’s still hasn’t stopped all the spam. Of more concern is that it reduced successful, after factoring for failed spam, by 3.2% (estimated). Maybe that’s not earth shattering, but if you’re in e-commerce and potentially you’re losing 3.2% of your revenue just to reduce spam, then I wouldn’t be happy.
Thanks to UX Australia for bringing this one to my attention.