I don't know if there's much to really say. Based on the opening weekend numbers, IM2 is poised to make over $300 million domestic, although probably not $400 million. Marvel's not going to complain about that. It's not likely to take the Summer, that's probably Toy Story 3, but it will certainly end up near the top.
It does kind of suggest though that we're seeing the cap of what an Iron Man movie can do. (And perhaps a non-Spider-Man Marvel movie.) The fact that Iron Man's foes are, by and large, unknown to the general public and not that interesting, probably doesn't help. Fighting more robots and guys in power armor is probably something they'll want to move away from. It probably als suggests that The Avengers build up is going to build off Iron Man, not bring in people that weren't already seeing Iron Man in the first place.