I think part of the challenge (indeed, maybe most of it) is trying to figure out exactly what the person is asking. Usually they know exactly what they want, but end up expressing it really, really badly. :) Some questions are so vague that all you can do is throw a bunch of clues and hope that some stick! :)

I like going beyond the question itself to see exactly what they are trying to accomplish. In other words, the question may be about some esoteric (or common) perl nuance, but I also like to try and give them some insite on code design, user interface, the cost (CPU, speed, readability) of what they want, alternative ways to do it, etc.

There is some risk as coming across as patronizing, or even insulting the person: after all, if they are asking about a regex, and you point out that the whole block around it is ill-written...

This might sound harsh, but I tend to assume that those who cannot carefully craft their question, cannot carefully craft their code. </alliteration>