I ran into just this annoyance recently, when Google threw the pictured CAPTCHA (and no, I never did find out what the third letter was) up (and on my own PC, to add insult to injury). Mildly annoyed, I fired off a media query to the Big G to ask if it had any plans to replace its CAPTCHA system with one that, you know, worked. Here’s what I got told in reply:
As you can imagine, we are trying to strike a balance between things that are easier for humans but still difficult for machines to break — obviously a CAPTCHA that is easy for a human to read will also likely be relatively easy for a bot to read. We do carry out internal and external testing to see how users are responding to them as we tweak them, which gives us data on which ones are working best for users, and while we do think CAPTCHAs are still effective (generally speaking humans are many times more accurate than the best bots we can detect) we’re also looking at more options, as we think abuse is only going to continue.
OK, it’s not a “we’ll have a fabulous new solution next Tuesday” answer, but at least it’s a glimmer of hope.