i was just guessing "neural" because i just assumed that 20q does handle some kind of 'link strength' between questions and answers so that a question that gets the same answer 20 times makes that answer more 'important' than some random answer given by a lost user. and IIRC, that was the basic mechanism of neural networks - that repeated 'stimuli' reinforce a 'link' - although i might be completly wrong (i still think it would make sense, though: wikipedia works because they assume that most users will actually do the 'good' thing, and the minority that do nonsense just dissapear under the flood of good stimuli/edits)

i somehow assumed q20 was open source or something, but i guess i was wrong. :(

one possible application i saw was for medicine, because looking over my gf's shoulder while she was studying, i noticed that a lot of diagnoses seem to be kind of fuzzy, and have a lot of interconnections with other symptons. (e.g. high blood pressure with diabetes is different from high blood pressure with only smoking), so i thought an 'intelligent' q20 thing would at least be a help for doctors.
on the other hand, i once heard that medical expert systems failed because too many diagnoses are actually made intuitivly/subconciously, due to the sheer amount of possible sympton-diagnose relationships.
ah well. would still be interesting, i guess - anybody know of some machine-readable symptom -> diagnosis graph?