I haven't ordered any signed books, just unsigned copies of the first three books at the same time, and those came pretty quickly. I'm sure the signed books take a bit more time to prepare, though, so if a few thousand people all decided to buy signed books when Jeph posted the announcement, that could result in a significant delay.
Also, Nov 27 was the day before a major feast holiday here in the US (Thanksgiving), which means your order might not even have been looked at until the following Monday. Now that it's over, everyone's getting busy with the Christmas season, going to parties and shopping for gifts, so that's another possible source of delay.
My best guess (only a guess, of course) is that Jeph got hit with a lot more orders for signed books than he was expecting or prepared for, and that's what's causing the delay.
