We are wondering about the same thing. The registration was supposed to open yesterday (Sep. 2) but so far the registration is yet to start. I suggest you keep on checking the official site, or better yet check out the updates on Adam Jacksons site dedicated to Macworld: http://macworldbound.com/
I responded to someone's comments earlier who was asking about when I thought they would open registration. Here's what I said,
". I generally leave IDG alone when it isn’t absolutely necessary. In fact, I only message them every 2 weeks or so with a specific list of questions and asking them to confirm some things. Early bird registration usually ends December 12th meaning you have over 3 months to register for Macworld at a discounted rate. It’s actually not a big deal to register when things open but I’m sure IDG appreciates your enthusiasm "
Paul Kent from IDG said registration should be online sometime next week (Monday or Tuesday) on the current "Your Mac Life" show - patience is a virtue.:-)
Plane tickets bought, hotel booked, conference registration done, vacation days approved. All that's left is to pack and get to the airport. All right!!