There is a simple and effective way to get people to vote that doesn't encourage the sort of insanity that ensued over night. This has been suggested MULTIPLE times, and yes, would require the score being hidden again. This is my best effort to show the value of an on going guess the score incentive.

UPDATE: Winning would not be linked to the vote (some good points were raised). You may want to give a design a 2 or a 5 but think it will score a 3.12, and should still be able to vote honestly while competing to win.

UPDATE #2: Don't do math early in the morning. Section on the money has been updated.

GUESS THE SCORE

Guess the score attached to every design would encourage people to not just vote, but to think about their vote and really examine the art. Instead of POWER SCORING though 400 designs in a mindless fashion, they would actually stop and look at the design, weigh the printability and the skill shown, and guess the final score. Each week when the designs are printed, you feature the guess the score winner on every shirt. This would accomplish a few great things that would largely benefit threadless as a business...

First, it shows the purchasing side of the community that they can win shirts by voting. What's this? Someone won this awesome shirt just by voting? *clicks link to start voting*

Second, it would encourage the blogging and submitting side of the community to start voting again. Most of us make up a good portion of your regular purchasers, so our input in voting, I would think, is pretty valuable.

Finally, it would motivate those who just sort of click through the voting alternating between 0 and 5 to actually slow down and vote with some thought. Slow down, dude, check out the art! Will this get a decent score? Will it print? You could freaking win a free shirt by simply slowing down and voting in a more thoughtful way.

In the end, all three of these things would increase the recurring visitation to the site, which, I imagine, is one of the main hopes behind the current incentive. And about that...

Honestly, lets think about the value of the current competition and compare it to the above guess the score idea. You are giving away $240 to one person for voting during one period of time. That equals out to about 10 full priced shirts, which covers a free shirt for 10 people instead of just one person. So instead of rewarding one person for whipping through the votes, you could reward multiple people each week, which will continue to create a buzz and an incentive for voting.

Do you see my point? Guess the score would provide you with somewhat less inflated total votes, but would provide you with more thoughtful voting and more recurring visitors. Added to the fact that you are spreading out the winnings, instead of shooting it all at one person, and continue to spread the word with each week. Every week people would see that they can win shirts by voting because you print new shirts every week (this would probably slowly increase voting). What you did for the 24 hours thing is already almost here and gone. In the end I'm pretty confident you won't get much of a return on the $240... not as much recurring votes and customers as you would from an on going guess the score incentive. And lets not forget that you are giving away $240 AND frustrating your artist pool in the same fell swoop.