I haven’t enabled captchas on my blog, partly because I think they’re annoying, partly because I really haven’t had trouble with spam comments that I know of (I must not be popular ;_;), and partly because the Blogger captchas weren’t accessible to the visually impaired–if you can’t see, and your browser can’t read the captcha to you (which is kind of the whole point of captchas, not being machine-readable), then you can’t post a comment.
I’m pleased to say that the last issue has been resolved.
Good for Blogger!
Sushicam has an interesting captcha system: instead of being some weird warped letter-number combination that you have to read and type in, it’s a math problem. I thought that was a unique solution, though I wonder how long it will take for spam proggies to be programmed to pick out the numbers and the math terms and figure out what the answer should be.