In a conference call, the White House clarifies what those reports about a three year time line were about. Although the phrase three years doesn't appear anywhere in Obama's speech, he will set July 2011 as the date when NATO forces will start handing over the lead of combat operations to Afghan force, and apparently begin to bring U.S. forces back home.
It's not at all clear, however, whether that is a fixed date--or whether it will be tied to unpredictable conditions on the ground. Update: I'm told that July 2011 is not condition-based, but that all decisions afterwards will be.
And along those same lines, a senior White House official speaking on background says: "This is the beginning of a process which is not yet defined in terms of the length of the process, or the endpoint." Sounds fairly open-ended to me--as it realistically has to be, given the uncertainties involved and Obama's apparent belief in the necessity of winning.
"If the Taliban thinks they can wait us out, then they are misjudging the president's approach," adds the official.