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.

Lisp is a functional-level language.
You have been banned from [spoiler]/prog/[/spoiler]!

I can see myself making such stupid mistakes for not taking the time to read the goddamn question.

There shouldn't be any problem using textual captchas, and making our own question bank would mean either creating millions of questions or letting some dedicated spammer try to exhaust the bank and solve all of them, but whatever, we'd have to implement one of them ans see which one works.