George Bush is a man of his word...he will never, ever, ever set a timeline to withdraw troops from Iraq. He will however set a horizon. Via Atrios:
President Bush and Iraq's prime minister have agreed to set a "time horizon" for the withdrawal of U.S. combat troops from Iraq as security conditions in the war-ravaged nation continue to improve, White House officials said here Friday. [...]
"In the area of security cooperation, the president and the prime minister agreed that improving conditions should allow for the agreements now under negotiation to include a general time horizon for meeting aspirational goals...The president and prime minister agreed that the goals would be based on continued improving conditions on the ground and not an arbitrary date for withdrawal."
In other words, nothing changed, just a little PR to make any agreement to leave troops in Iraq that Bush signs a little easier to shove down the throats of the American people. And remember, to John McCain, the horizon can be 100 years from now because after all, bringing home the troops is "not too important" to him.