I'm not that worried about Orlando and Washington. While I'm not going to look it up right now, I'm fairly certain at least some of the losses we had against them came with either Allen or Garnett out.
I might be in the minority here, but I don't think Bynum is going to help the Lakers nearly as much as some do. Yes, he should make them have a better interior defense; however, it may not be as much as some think. He's still very young and it remains to be seen if he can grasp the concept of team defense like a guy like Perkins. And that's not even factoring in whether a guy like Gasol or Odom can buy into it as well. Offensively, I think Bynum is actually going to make them worse. Throwing him into the mix, takes Radmanovic out. And while I think Radmanovic is a bum, he did spread the floor with his range. Now, the Lakers will most likely start a front court of Bynum/Gasol/Odom. None of them have range. It's going to make it very easy for opposing teams to pack the defense in the middle, making it hard for any of them to post up and hard for Kobe to get to the hoop. I think their dynamic offense of last year could really stall as a result of this.
As many of you said, the Cavs probably worry me the most. LeBron is a tough cover, and he was probably the one player that Posey was most useful against, so that hurts. They also have good outside shooters, which makes it hard to clog the middle. On top of all of that, they have excellent size up front in Z, Wallace, Smith, and Varejo. That really hurt us last year: they shot over us at times and our guys had trouble finishing around the hoop.
Still, when it comes down to it, I think the Celtics still have the best starting lineup in basketball. Rondo should take it to a new level this year, as should Perk. If they can all stay healthy, we should be able to get by with our bench, regardless of how it pans out.