AFP is reporting that an American F-16 was hit by small arms fire over Paktia Province in eastern Afghanistan over the weekend. The damage to the jet was severe enough that the pilot decided to jettison all external stores (drop tanks and bombs) before returning to Bagram Air Base north of Kabul.
Although a number of rotary wing aircraft have been shot down or damaged by ground fire while operating over Afghanistan, tactical jets have been basically untouched by the enemy since the first airstrikes started in October of 2001. The Taliban don't have much in the way of an integrated air defense system (a la Desert Storm-era Iraq), and jets can usually remain out of the reach of shoulder-fired surface-to-air missiles (like Stingers) and small arms fire by flying above 10,000 feet while delivering GBUs or JDAMs.
So, in order to have been hit by bullets, the F-16 pilot had to have been flying pretty low. Pilots generally fly low for two reasons: A "show of force" pass or a strafing run. Non-precision ("dumb") bombing can cause a pilot to bottom out at low altitude, but it's unlikely the Falcon was carrying other than smart weapons, even for a close air support mission.
The Taliban claimed to have downed the F-16 and pictures have emerged of them posing with wreckage, but the U.S. military responded with the following statement: "On October 13, a US F-16 encountered small arms fire in the Paktia Province in Afghanistan. The surface to air fire impacted one of the aircraft's stabilizers and caused damage to one of the munitions."