I did one with Avid Treasurers this past week, and it has generated 2007 views so far, which I'm really thrilled about. It generated an explosion of views and favorites in my own store (although no sales). I haven't yet polled the other contributors to see how they've fared so far. But, I will post here how it went once it's done on March 1st. I definitely recommend doing it. If anyone else decides to do one, let me know. I may do another one myself too.
With regard to shipping, my plan is that all of the artisans will ship their items individually and pay for it so that the winner doesn't have to pay anything. But, I suppose you could put that into your terms for the winner, that they'd pay the shipping. I don't advise it though. You'd have a 'winner' paying 16 separate shipping fees. What a pain. Best to think of it as a marketing expense.