From the psychology literature, from a psychology major--here's why I'm a firm believer that we could still be fielding a high caliber defense this year:
The learning curve. Initially, performance is low. But as the number of trials continue to increase, learning steeply increases and performance improves significantly until plateauing; where the number of reps doesn't significantly improve performance.
Applying that to our situation, we have a lot of players who played their first snaps at the collegiate level last night. It should have been no surprise that the product we were going to see wasn't going to be a very good or even average performance. But what we did see was the defensive line (VV and RG44) pushing their offensive line back, getting pressure on Brett Smith, forcing him to dance around (which not all QBs can do by the way) and throw the ball away, sometimes forcing the ball into a tight window. What we did see was the coverage making two interceptions and breaking up a handful of passes. What we did see was our safeties and corners being there on most of the passing plays.
Yes, we did see the silly mistakes, the missed tackles, the inability to get to the QB despite getting pressure on him, the linebackers failing to adjust to the motion. But we also saw a lot of good things, a lot of athletic plays, suggesting that the plateaus for these players are MUCH higher than the defense we had last year.
What needs to happen is for them to start making that jump, it will happen, just a matter of when--it might not be next week, it might not be by the end of the year. For the fan's and Bo's sake, I'm hoping it is before B1G play starts (we can beat So Miss and SDSU with our offense, and a loss to UCLA won't be the end of the world).