IMHO captchas still have their place. Any type of turing test would require intervention by the user. I dunno how low the threshold of annoyance is for most users, but I tend to think that "reproduce this text" produces a lower cognitive load than, for example, "what is 4 + 3." If your text is extremely jarbled that's a different matter... note to self.

Picture matching is a viable alternative and can reduce cog load, but it also increases the time between captcha and the intended action. I use a 3-character captcha. We'll see how that holds.