Question Author
I was thinking that it might allow people to assess how qualified posters are to answer a question. I agree, however, that it would probably be open to abuse and consequently impossible to police.
Some of the health and legal questions, for example, are quite serious and, once you sift out the drivel in some of the replies, you are often left with very intelligent suggestions which really look as though they are written by people who know what they are talking about. Confirmation of this would be reassuring.