Here are some random links that demonstrate (I believe) the growing popularity of the NXT and its potential sales for the upcoming 2006 holiday season. I can't find any information on whether LEGO expects to sell out, but if you're considering buying one, I wouldn't wait until December.
Impact Labs - Top 12 Toy List
FamilyFun - Toy of the Year
Popular Mechanics Breakthrough Award
FAO Shwarz Toy Innovation Award 2006