From a story on the search for bin Laden at ABCNews.com:

U.S. special forces are stationed across the border [with Pakistan] in Afghanistan with approximately 45 checkpoints should bin Laden head there, but authorities said there are many unfrequented routes and it is impossible to seal the entire border.

Special forces in Afghanistan, however, are not as specialized as they once were, [former CIA counterterrorism chief Vince] Cannistraro told ABCNEWS. This specifically hurts the hunt because, he added, in order to deploy intelligence resources to collect information on bin Laden, the U.S. needs Arabic speakers.

"If you've drawn off many if not all of your Arabic language resources and sent them off to Iraq you're shorthanded in terms of dealing with intelligence collection problem of fixing bin Laden's location," said Cannistraro. "So there are fewer resources to deal with in trying to basically find and capture, the principal leader of a terrorist organization that's killing Americans."

(Emphasis mine.)