I was encouraged by what I saw in the SAS game, and the first half of the ATL game. I think in the practices before the Spurs game, the coaches and/or vets drilled into the others (read new guys) that it was time to start playing "Celtic" basketball....now. Krstic came out and played - for him - harassing defense. The bench guys played hard, and Rondo played like Rondo.
Before the arrival of KG and Thibs, we were far from a defensive juggernaut. Remember how we worried about Ray being a defensive liability when that trade happened? How many people were talking about Perk as a great defensive center prior to 2007? How did the Bulls go from a mediocre to a great defensive team? The system, and a focus on and commitment to defensive makes a huge difference. The problem is we don't have much time with the new guys, as it takes a fair amount of practice team, which we haven't had nor will. But I think we can get better, enough so to be a strong defensive team.
More than anything, I think having JO+Shaq in the middle for 25-30 mins a game will help toughen us up as well.