Both the Army and USMC have issued the 590A1 for various purposes. I just returned from my 7th (and hopefully final) contract as LE/security trainer overseas. Been to the Balkans and sandland. Shotguns are very handy, especially in urban areas. I have seen a couple of Winchester 97 trench guns being carried by US personnel as well as some other pump guns. Some weird stuff can be found in supply rooms, particularly Reserve and Guard units that have horded stuff for the last century or so.
Some interesting differences in Iraq and say Kosovo/Serbia: In sandland the BG usually spray and pray with small arms, the preferred weapon being RPG and IEDs and the ever popular suicide bomber, with or without car. In the Balkans they had some BG who were really dangerous snipers, in Iraq I felt safe from rifle fire at about 300 meters away, in Kosovo you could get sniped from 8-900 meters easy. Some of those guys could shoot!
In Iraq the locals seem to respect shotguns and pistols more than the rifles, maybe they really think you are more likely to shoot them with the close range weapons?