1911's- The Marines who belong to MEU's (and were among the first to be deployed in Afghanistan), are an amphib ship based "package" of troops that includes ground troops, medical and support personnel,and even light air defense (LAAD) batallions, have access to 1911's tweaked by the armorers on board as of recent times, though I've only seen Marines with M-9's in my travels.
5.56 effectiveness- We are our own worst critics, though I can support the short barrel, lower velocity nay-sayers, I agree with the above poster about the Soviets and the 5.45 round. We've read in the 80's that the Afghans reported how effective the 5.45 round was when the Soviet's started to use it against them, and how they sought out AK-74's over AK-47's to gain this similiar advantage, without question, yet we doubt our own cartridge every time a bad report comes out.
I think the US military understands the need for a mix of 7.62 and 5.56. The M1 carbine had plenty of critics in WW2 and Korea, where oone could hear stories of hitting heavily coated N. Koreans at a distance with the .30 Carbine Ball ammo and having little effect.
Ultimately the 7.62 round rifle makes alot more sense for defending fixed positions in my mind, as you can keep a stockpile of ammo next to you, but for mobile situations where you're dropped in and have to carry everything of your own for days, the 5.56 round has it's place.