Reaction time is good in general, but rather useless in the traditional IQ tests, i.e. culture-neutral multiple choice pattern-based questions. If you are 25% faster than your neighbour it gives you the benefit of the additional 25% of the reaction time, not total answering time, which is usually much larger in the context of IQ tests. Or nearly any test, for that matter.
Oh, sorry if I wasn't clear. Reaction time is strongly correlated with the overall speed of brain function. So it applies to other brain operations too.
Normal IQ tests should also contain a computerized part where you have to react and solve problems on a computer with a time limit. Last time I did that, they still used Win2000, but I can only imagine this increased.
