Three weeks back and three Leno Tonight Show ratings wins. Jay was steady last week, but Dave slipped a tenth of a ratings point. Note that the Thursday and Friday airings of Letterman's Late Show were pushed late by NCAA basketball and were not included in the weekly average for the week ending 3/19.
For historical reference, here are last season's 18-49 season-to-date averages through March 20, 2009:
NBC “Tonight,” 1.4 adults 18-49 rating
CBS “Late Show,” 1.1 adults 18-49 rating
And for additional historical reference, here is the tally of the adults 18-49 ratings for the entire run of Conan O'Brien's Tonight Show, except the final week of repeats prior to the Winter Olympics.