As of August 28, 2011, Red Sox were 82-51, 1st place, 2 games up on Yankees. A bit ahead of this years' pace(79-55).
They won 8 of their final 29 games, finishing out of the playoffs. We still don't really know why that happened--except the pitching went sour.
Nobody expects it to happen again. This is a different team. But it's a reminder of what can happen. The division races can be changed in September by teams turning hot or cold.