Zach Lowe wrote this today -
http://grantland.com/the-triangle/rajon-rondo-trade-dallas-mavericks/
Lowe is echoing everything I have been saying since I heard about the trade. While everyone is crowning the Mavs champions, you have to acknowledge the fact that the league's best offense might have just handicapped itself with a ball-dominating offensive liability.
What he doesn't mention is how the Mavs will improve with Rondo. They will improve on the defensive end.
While Rondo isn't a very good defender anymore he is elite at two things at the PG spot, passing and rebounding. Rondo is rebounding a higher percentage of defensive misses than every player on the Mavs besides Chandler. The Mavs are 29th in the NBA in defensive rebounding. You can expect their defense to improve when they are giving up significantly less offensive rebounds. Rondo also forces a lot more turnovers than any of the guards he is replacing.
So I guarantee Rondo helps the 22nd defense in the league by moving Dallas from the bottom of the NBA to the middle in defensive rebounding.
Rondo is a high variance player who will win games with outstanding play in the playoffs. In such a tight Western conference the difference of one or two big games he can provide could equate to a finals appearance instead of a first round defeat. They are currently 0-6 against the teams ahead of them in the West, Rondo shows up on the biggest stage, it could be exactly what they needed.