For me, i guess it depends on what you mean by "obliged." If you mean, should there be a rule that everyone who enters
has to vote or be disqualified, i would probably answer no. But, in my opinion, anyone who enters is, in some general moral or philosophical sense, obliged to vote.
This was reinforced in my mind by the December competition.
I came second in that competition (results
here). As you can see from the scores,
snadge beat me by three votes. If you searched back through the thread to find my vote, you would see that i gave
snadge's picture my top vote, thus giving him exactly the three points that constituted his final margin of victory.
Had i refrained from voting that month, i would have ended up in equal first place. Also, knowing that
snadge was a frontrunner when i cast my vote, i could have left him out of my winning three just to increase my chance of victory. But i think that the friendly nature of this competition, and the camaraderie of urban, puts a premium on honesty.
Given that no-one ever votes for their own picture/s, and that doing so would probably be seen as rather poor form, anyone who refrains from voting at all is, in fact, giving themselves an advantage by refusing to parcel out points to his/her competitors.
Before today, i had never seen that earlier discussion about voting, the one linked by
Firky on the first page, but i must admit i was rather put off by those who argue that choosing from 100 photos is too hard. Sure it is, but so is taking a good picture. And i think that if you're willing to submit a photo for consideration, then you need to be willing to give the pictures of other people your consideration as well. After all, if we all decided that it was too much effort, there'd be no votes at all, and we could rename the threads "March photo gallery" instead of "March photo competition".