He's not the first in late night tv to have that happen to him (see Letterman, David) but at the end of the day I feel Conan's Tonight Show will outlive Jay's talk show in primetime in how much it actually impacts culture.
I watched a couple minutes of Leno the other day and the big comedy bit was Jay finding "wacky" items on Ebay then seeing if they actually sold or not. Really. And it isn't like Jay doesn't know what's funny. When he used to sub for Johnny Carson he was genuinely humorous. But then he got the Tonight Show and got safe, safe even by the standards of network tv. And safe = stale.