I'm all about comparing TV ratings, but last week's Tonight Show was both (a) delayed every night by Wimbledon coverage, and (b) in repeats. As such, I don't view last week's ratings as particularly indicative of anything. The weekly chart is below for those who were waiting for it though.
Perhaps caused by the lack of head to head Tonight Show competition, Letterman's Late Show was up a tenth of a point vs. the prior week.
The chart shows the late night weekly average adults 18-49 ratings for 2009 and 2010.
Note: The week ending 7/2/2010, the Tonight Show was in repeats, and was delayed by Wimbledon coverage.
No more chart of the sequential weeks comparison between Conan and Leno. That chart was always a bit apples/oranges because of the different seasons. While before the calendar runs of the shows overlapped we had to make do, now that we have some of the same time period to compare, the sequential chart has been retired.