Remember that DSi XL that's coming out next week? Well, I hope you didn't spend a bunch of money in the DSiWare store with your regular size DSi. Yep, turns out that you can't transfer games to your new hand-held. That really sucks.
Nintendo did confirm that this is a known issue, and they are looking into the problem. At this time though, they don't have an ETA on when exactly you'll be able to transfer games. The issue lies in the way the store is set up, and the fact that purchases are tied to a hand-held device, instead of an account.