In response to Stephan: You weren't part of the forum at the time, but there was a Paint.NET logo contest in Janurary. It lasted over a month and we ended up with more than 15 users joining in and over 30 logos to vote on. My point is that you can submit multiple skins (a maximum of about 5), have time to go back and fine tune, and have a decent competition (with more than 4 entries) by the end of the month.
Another reason to do widgets is because you can actually download and use them-- not just admire them. You would be able to upload them to the Konfabulator Gallery and DeviantArt.
@Firefly: The OS talk was about creating a screenshot from scratch, not a theme.