no doubt that this will be one of the top grossing movies of all time, possible top 3. Do I think it will do long term Avatar numbers? Not so sure. Avatar was sold and billed as the first "next gen" 3D movie, and the crowds came flocking for that reason. Now with everyone and their mom having a 3D post conversion, the novelty has warn off.
Personally, I am going to be seeing Star Wars in 2D, mainly because it wasn't shot with 3D in mind like Avatar was. Also, because I'd rather save the extra $5 on that small popcorn.
If I want to see 3D I'll go to UOR..ha ha.