On a scale of respect I have for a person from 1 to 10, 10 being Abraham Lincoln, Jimmy Kimmell has gone from about a 2 to at least a 6 in the past few days.
Also, I don't think Leno and Kimmell were ever really that friendly. I remember one Kimmell comment once, I'm not sure if it was in an actual interview or if it was an off-the-record statement, where he said something along the lines of Leno set comedy back decades when he got the Tonight Show gig.