Yes, I'm trying to avoid even writing about this stuff, but...
I think the primary thing that an Obama run does is kill what was the long held conventional wisdom that the race would be between Hillary and someone who manages to emerge as the Not Hillary. Obama could've been the Not Hillary if he'd gone that path, but his knee-jerk tendency to triangulate has made that unlikely. So, right now we're looking at Hillary, Obama, and NotHillaryOrObama, who will probably be Edwards.
And all this could change in a month.