Why the US will never abandon Afghanistan
A lot of people think that the US is looking to pull out of Afghanistan as soon as possible, and that we won't have the staying power to stick around. They dismiss
pledges of aid as short term contributions that the US will eventually tire of. These people need to look at a map:

See that nation next to the upper right finger of Afghanistan? That's China. There's
no way the US will give up a base right next door to the only power that might present a serious threat to the US military in the years to come. That's why we'll be in for the long haul in Afghanistan.
Update:
See also this excellent
piece on China's development as a superpower. The following
passage is of particular importance:
Given current trends, China could emerge, by 2015, as a formidable power, one that might be labeled a multidimensional regional competitor. Such a China could credibly:
- exercise sea denial with respect to the seas contiguous to China
- contest aerospace superiority in a sustained way in areas contiguous to China's borders
- threaten U.S. operating locations in East Asia with a variety of long-range strike assets
- challenge U.S. information dominance
- pose a strategic nuclear threat to the United States.
Obviously, an airbase next door could only help in combating China's air superiority. India would likely cooperate with us against a militaristic China, but better to hedge our bets.