Afghanistan isn't called the graveyard of empires for nothing.
Want my take on it?
(1) Don't go there.
(2) If you're already in there, get out.
(3) If you absolutely have to go there, go in fast, do your thing, and get back out.
That's all. And that's what the USA should have done, post 9-11 -- gone in, smashed the Al Qaeda training camps, captured or killed Bin Laden, and gone out again. And left a little note on the wall saying that they'll be right back should they attempt to set up the camps again.
I understand why you guys chose to stay -- partly in order to keep the Taliban down and stop the Qaeda from setting up shop again, and partly out of humanitarian motives, to set up a decent government in Afghanistan. That's just not a practical proposition. The only person in history who has ever managed anything like it was Alexander of Macedon, and Bush was no Alexander of Macedon -- and, as much as I like the guy, neither is Obama.