When I post an answer to a brand new question I usually find that someone else has submitted that same answer just moments before. (Matt Hamilton, usually ;-) )

What I've started to do lately is (i think) the right thing.

If I notice that another answer predates mine, and that I add no value over it, I immediately delete my own answer, and upvote the other guy.

I recommend that you too do the same. Otherwise the message will be diluted.

Similarly, if after posting your 'answer' you realise that you are in fact wrong (and you've just misread the question) -- you can actually delete your answer.

Is this reasonable?

(The reason why I'm writing this down is because it feels completely counter intuitive to delete your own stuff. But it really saves everyone time and effort)