Check these stats...
2008:
22nd in points allowed/game at 23.8
20th in yards allowed/game at 334.3
12th in passing yards allowed/game at 202.8
26th in rushing yards allowed/game at 131.6
At year end, 15th in penalties on defense at 89
At year end, 15th in penalty yards on defense at 721
14th in 3rd down defense at 38% conversion
At year end, 25th in sacks at 27.0
At year end, 3 way tie for 3rd in INTs at 22
At year end, 2 way tie for 28th at fumble recoveries at 6
2009:
12th in points allowed/game at 19.5
1st in yards allowed/game at 281.5
7th in passing yards allowed/game at 192.5
4th in rushing yards allowed/game at 89.1
4th in penalties on defense at 57, on pace for 83
3rd in penalty yards on defense at 424, on pace for 616
4 way tie for 1st in 3rd down defense at 33% conversion
17th in sacks at 23.0, on pace for 33.5
3rd in INTs at 18, on pace for 26
6 way tie for 7th in fumble recoveries at 9, on pace for 13
All of these were compiled from stats at NFL.com. Can we seriously expect any more improvement from this defense? Sure, it'd be nice to get some more pressure on the QB, but even then we're on pace for 5.5 sacks better this year.