While some folks are still focusing on whether Jay beats Dave (as if NBC gains anything other than PR value from "winning"), NBC's business is based on increasing (or slowing the decrease in) their ratings and the advertising revenue tied to them.
By that metric, NBC made an even ratings trade vs. last year's premiere week, as Jay Leno's Tonight Show adults 18-49 ratings tied those of Conan O'Brien's Tonight Show on a calendar week basis (2010 vs. 2009) for each season's broadcast primetime premiere week.
Leno's Tonight Show for the week of September 20-24 averaged a 1.0 rating with adults 18-49 the same as Conan's Tonight Show ratings for the comparable calendar week last year.
Letterman's Late Show scored at a 0.9 adults 18-49 rating for premiere week.
Remind me again why Jay beating Dave is important for anything other than PR or pride?
The chart shows the late night adults 18-49 weekly average ratings for 2009 and 2010.
Note: The week ending 7/2/2010, the Tonight Show was in repeats, and was delayed by Wimbledon coverage. The week of 7/9/2010 the Late Show was in repeats, and both shows Monday airings were excluded because of the holiday. For the weeks ending 7/16-8/6, Late Show was a repeat only on Friday. The week ending 8/13, Late Show was encores all week. Both Late Show and Tonight Show were repeats the week ending 8/20. For the week of 9/3/10, Late Show ratings were based on four days only. Note for the week of 9/10/10 NBC's Thursday telecasts were delayed by a primetime NFL overrun. Friday's "Late Show" was an encore, Monday results are excluded from these averages due to the Labor Day holiday. Late Show was in repeats the week of 9/17/10.