I doubt NBC is anywhere near panic mode yet, but it must trouble them more than a little that, ratings-wise, Nightline is beating the new Tonight Show so frequently now.
I suspect this situation is only going to get worse: we just wrapped up one serious election cycle, but there's another one coming next year, and then the 2012 campaigns heat up. This means folks are going to turn more to news-oriented programming than entertainment-oriented programming. If Conan can't win now, he'll be hard-pressed to top Nightline down the road.
Another sign of trouble:
A lot of people -- a LOT of people -- tuned in to check out the new host his first week. So much so, in fact, that NBC proclaimed him the new "King of Late Night" in an episode of PR-fueled hyperbole that ended up backfiring on them a little (it takes more than a week to claim such a crown, after all).
It was only a matter of time before those numbers dropped, but they've dropped noticeably and regularly. This means that people have sampled the new host and aren't thrilled with what they've seen. Some of them may return, certainly, and it would be as premature to proclaim the Conan O'Brien experiment a failure as it was to proclaim him the new King of Late Night.
But does anyone else get the impression that Jay Leno's Tonight Show tenure might not be done quite yet?