Just last week a few stores in the general "North-Eastern" area of the US was breaking the street dates for Modern Warfare 2, and now, as Destructoid reports, Gamestops in Jersey City, New Jersey are breaking street dates for Assassin's Creed 2 and Left 4 Dead 2. This seems more like a trend than cooincidence now.
Calls to the specific stores 4627, 4260 and 6005 by Kotaku revealed "it was because a local independent retailer had done the same". Could it be a single retailer in the area that's large enough to warrant three Gamestops selling early to compensate? I have no idea, but if you're in the area give your Gamestop a call, and they might have a copy for you.
Being the inexperienced young'un I am, I wonder "Why don't stores simply sell once they get their inventory?" It's always been Tuesday, and in a few rare cases other days of the week. I read once that it was because shipments usually go out the Friday before and arrive around Sunday/Monday, so why hold off the extra day? Besides the obvious "we've got it, you can't have any" making people wait, get excited, etc.
Either way, Assassin's Creed 2 looks great, and Left4Dead2 looks gross (in the best way).