Its a very good idea Devonpond.. We had a really good online photocontest a few years back..They take alot of work though and its often hard finding members to shoulder that burdan..... I'd entertain it here for sure though if the interest was there, and help in both the organizational aspects and the judging.
This is something that we have kicked around in the university section, but again... its hard to find the judges.
Consider it under consideration!
-al