While the sky isn't currently falling because of the two losses to LA and SA, what's troubling is the Celtics' current state vs. the current state of opposing teams. The Cavs are better than last year with Mo Williams on board and a full year with Wallace, West, and Sczerbiack. The Lakers are better with a full year of Pau and the potential return of Bynum by the playoffs. The Magic were better than last year before Nelson got hurt, and still might be better than Detroit was last year (since Howard is a beast).
As for the C's? The only two really reliable bench players from last year's playoffs are gone. While everyone likes to focus on Cassell's poor play in the playoffs, the only reason he got PT to begin with was because House wasn't realiable. Powe and Baby had their moments, but ultimately their biggest weakness (size) will be exploited as we once again will probably have to go through the monster front lines of Atlanta, Orlando, Cleveland, and either LA or SA to win #18.
This isn't good.
Could they win it all with what they have now? Yes, but they're gonna need to be red hot and need for Cleveland and LA not to be. Could that happen? Sure, the Giants beat the Patriots after all. However, it could be tough over the long haul.