From the woot site about the cart:
2. Real talk: we only ever had that $5 All You Can Ship in a Day promotion going because we didn't have a shopping cart. So now that we have a shopping cart, we're getting rid of it. Standard shipping is now $5 per order — just get all your stuff in one order, and it's basically the same thing.
3. How does this affect Woot-Offs? Well, you'll have to stay on your toes. Stuff is going to sell out and sell out quickly, so you'll want to check out as soon as you can. Yes, that means you'll pay for shipping more than once if you end up buying more than one item, but the truth is we sell stuff at such stupid low prices in the Woot-Off that you're still getting a good deal.