It's amazing to see just how much Rondo's defense has had an overall impact on the team defense of the Dallas Mavericks.
Here's some eye popping stats.
Mavericks before trade ORTG 113.6 (#1)
Mavericks before DRTG 105.1 (#19)
Mavericks after trade ORTG 109.8 (#7)
Mavericks after DRTG 99.6 (#6)Basically what everyone expected to happen did happen. Rondo's presence has diminished Dallas's offense, but he has more than made up for it in the improved team defense, a jump of 13 in the rankings.
Also, his individual defense has improved as well. Before, he was a minus defender at the point guard position with the following stats

Link:
http://stats.nba.com/player/#!/200765/tracking/defense/?DateTo=12%2F19%2F2014&DateFrom=10%2F01%2F2014Now, he's playing great defense against some of the best point guards (John Wall, Kyrie Irving, Russell Westbrook) in the league over the span of his 8 games with Dallas with the improved stats below.

Link:
http://stats.nba.com/player/#!/200765/tracking/defense/?LastNGames=8In particular, his 3 point defense has been outstanding. He's fighting harder through picks and using his length to disrupt the opposing guard's rhythm. It looks like when properly motivated, Rondo can still play an elite level of defense against the NBA's best at the PG position.