I don't get the Leno hate, really. He hasn't really done anything wrong so far.
Six years ago, he said he would hand over
The Tonight Show to Conan, no fuss no muss. Come six years later, instead of retiring and giving Conan his time in the spotlight, he's poised to steal the show back from him (even though his own ratings at 10 PM haven't been great).
No matter how you cut it, it's pretty douchey behavior to say you're gonna let someone take a job and then steal it away from them again.
Add to that, Jay had to sign a new contract to get back the Tonight Show, it wasn't part of the existing one. in other words, NBC essentially said "hey you want to take over Conan's show?" and he said "YES!!!" - you notice that new contract was actually signed days ago. There was no time wasted.
Seriously he pretended like he was Conan's buddy, and then jumped at the chance to throw him out. That's pure asshole behavior. We've gotten to this point where it's sooo ok to act like a douchebag if it benefits your career. Because that's all there is to life. Yes, in his heart Jay didn't really want to leave the tonight show. We know that. Going out of your way to screw someone over like that to get what you want says a lot about you.