Spam Prevention Techniques (ideas)

So I've been thinking of various spam prevention techniques, from stats & NN to NLP, but, how would you all feel about textual challenge questions?

Either questions I can make up in my spare time about programming (i.e., "Lisp is a ____-level language."), or textual captchas? So you could still post through links or whatever, and nothing would ever leave my server, but it would make it a lot harder to automate posting.

>>9
Neuro-linguistic programming? What the fuck?

Neural networks have nothing to do with neuro-linguistic programming. The latter is some pseudoscience brainwashing technique.

NNs are matrix-vector stack multiplications with a "multi-layer perceptron" model loosely based on the way the brain itself works on a neuroscience level. They're used for data classification and prediction. Feeding a shitload of spam into a supervised NN and training it will allow it to "figure out" what spam looks like, in a sort of statistical way.