If Jermaine O'Neal can play at an acceptable level in the play-offs, I think Boston needed to do this trade.
I didn't like their chances against Miami with a wing rotation of Paul Pierce/Ray Allen/Von Wafer/Delonte West. Regardless of the strong interior and help defense in the last reg. season win, I think that was fools gold. I also don't think guys like Butler or Parker would change anything significantly. Not with the kind of wings Boston will face.
I also didn't like that their best small-ball line-up was Pierce at the 4.
I believe Jeff Green is a very above average defender at the 3, especially versus the big wings Boston will face in the playoffs: LeBron James, Carmelo Anthony, Luol Deng, Hedo Turkoglu, maybe Durant.
I think Jermaine O'Neal is more important than Shaq. The other day I noticed in Synergy that Jermaine was one of the best post defenders in the NBA last season and spent quite some time looking at his clips. If he can play at that level this season, I don't think the Celtics interior defense got any worse. I'm slightly worried about the rebounding and, in fact, I'm a bit worried that the offense got worst because of O'Neal trying to do too much, unlike Perkins.