Many of you have been asking, so here's the answer: the sweepstakes winners have not yet been chosen. To give you an idea of how many there were: I made a text document of all the entries, and the file size of that document was 22MB.
The entries have been divvied up among staff and we're poking through them, finding the winners and formatting all the answers for sending to JKR. As soon as we know more, so will you. :)