I was critical of Late Night with Jimmy Fallon when it debuted, however I had the chance to watch it every night last week (I stayed up to watch Conan every night, and then just stuck around) - and I must say the show is noticeably looser and funnier.
I saw two things that especially made me laugh - Head Swap (which I understand is a recurring bit), and Neil Young performing "Pants on the Ground" (above; a song made famous on American Idol last week).
Even Fallon's monologues - which are sometimes devoid of laughs - don't bother me as much anymore.