I sympathize. Many times I see a question I know I could answer (and thus advance on the road of Monkly Enlightenment), but The Usual Suspects have beaten me too it by a minute or so.
I personally believe it should not be taken as a competition, by any means, and thus I do not sympathize. If you know you can answer, just do it: that yours does not come as the first answer right below the OP does not matter. It may still be better phrased than a similar answer by the Usual Suspects, or give more details, or expand on the subject. Of course, if an answer has already been given and you saw it, then don't repeat the obvious part of it -I see this clearly happening every now and again, and it just hits on my nerves- but just point out the additional details, etc. (if you have them) perhaps specifying "in addition to what the Usual Suspect said..." as a sort of acknowledgement.