One major problem of captchas is that usually blind users can't solve the captcha. So you effectively lock out disabled persons from your website, a fact that is rarely mentioned in association with captchas. I think disabled people have enough problems already, there's no reason to further annoy them with captchas (I'm even annoyed by them as a not-disabled person).

Although it's not about programming, I'd recommend "The design of everyday things" by Donald A. Norman. It gives a good idea on how to design user interfaces (including, but not limited to software). It's really well-written and nice to read, wether or not you know something about user interface design.