I've been to a couple full games, quite a few 4th quarters and there's always been tons of fans that stayed after the game was over.
Also, Brett gained a LOT from the City, State and organization. Let's not make this sound as if it's one way here, that's a little naive.
They all benefited from one another.
Even with that said, I still (as I said first) don't really agree with the booing of him leaving Lambeau Field. Before the game, during the game, of course. It's hard for me because I think the Vikings QB should be booed his ass off, but I don't think Brett Favre deserves it. However, he reveled in defeating us last year, both times more so than many other wins I've seen him in. That bothered me, but also since I don't know everything that happened. I thought, well, if you were wronged Brett, I'm happy for you. If not, I hope we beat your ass next year!
In my opinion, he got his, we got ours and I think we should have left it at that, meaning, booing was not really needed. I don't think he ever bad mouthed us Packers fans, in fact, he said we were the best fans, while wearing Jets and Vikings uniforms he's said that.