Hawkeye would be considered an exceptional archer even in the eyes of the world's best where a hit at a range of 150+ meters would be considered excellent shooting.
Most bow hunters shoot at targets averaging 35 to 75 meters away. Target archers can shoot at ranges of 100 -200 meters. (But targets don't move.) Was Clint Barton superhuman in his ability? Most of his shots made against targets within the interiors of buildings or onboard the helicarrier, were not extraordinary or outside of the realm of possibility.
The farthest accurate shot in archery under FITA conditions was 200 m (656 ft 2 in) by Peter Terry (Australia) at the Kalamunda Governor Stirling Archery Club, Perth, Western Australia, Australia on 15 December 2005. He hit 2 ouf of 6 on a FITA 122cm target. He used a 'compound bow'. --Guinness Book of Records
Where Hawkeye was at his most awesome was during his shots above the city. Were these shots impossible? No. But after a 150-200 meters, shooting targets moving in excess of fifty miles per hour, he starts becoming superhuman in his ability.
But if we consider the Marvel comics' history of the character Hawkeye, he has been training since he was six years old at a circus. He would learn to shoot from the most difficult angles and from the most difficult conditions, including shooting from the back of a bicycle, riding on a horse, shooting at tiny targets, shooting at moving targets. He was trained by both Trickshot, who was arguably one of the only archers better than Hawkeye and the Swordsman, another martial artist whose skills were legendary on Marvel Earth #616.
If we consider Hawkeye is about 20-30 in the Avenger's movie, he has been shooting daily for fifteen to twenty years. He practices everyday with weighted arrows (to familiarize himself with his arrow payloads) uses the finest bow technology money can buy, arrows balanced and made with the highest quality precision crafting.
Then consider he is a super-assassin who was likely given even MORE training, more discipline, military tactics, strategy and we can assume a highly trained individual who has used his weapon of choice on a battlefield against men with GUNS. His sense of the battlefield was excellent and was able to assist Iron Man by sharing the information about the limitations of the Chitauri vehicles.
In addition to all of his other skills he is a trained observer, so it would not be unreasonable to assume a certain level of what would appear to be superhuman proficiency. Although when he was making shots and not looking, I would just call that showing off.