Ok, this thread appears to be deviating somewhat from my original intention, but that's cool as I think it's moving in an interesting direction.
With regards to the 'judging' how about if it were up to the person that set the task for that month to decide on the winner? Obviously they wouldn't be able to take part in their own task, but that's not always a bad thing..... A poll would be another good option, peer review is always a good way of telling how well you're doing. Given that a poll can be added to a thread at any time this could be added after a specified time has passed and then people just vote on the submissions (also saves cluttering everything up with loads of threads). Once the voting's over and the winners announced we could then allow alternative solutions, or discussions of the solutions that have been posted.
On that note, how would the submissions be handled? If they were posted up as people put them in using the [spoiler][/spoiler] tags then other people could potentially copy the entries.
Also, there's the issue of people submitting stuff that isn't actually their work.
I like the idea of multiple classes (might give me a chance of winning something
), but fear it could be complicated to organise and judge.