I saw the movie last week. The portrayal of the Marines are not too far off. As an Army Officer I have seen my fair share of comaraderie such as that portrayed in the movie. I know quite a few Marines (my twin brother) who say a lot of the Marines are like that.
On a different note, I agree with BigJon about the character flaws and such besides Jamie Fox but you have to also remember the majority of the ages of the platoon are 18-20 and right out of high school. All Soldiers and Marines are portrayed as steely eyed killers but you have to remember most of them are young and experiencing more then the average person ever will. Talk about sensory overload. Jamie Fox's character had been in the miltary over ten years and had seen combat before.
Sorry about going out to left field. The movie is funnier then hell for the first hour and then pretty boring after that. Well worth the matinee price at the theaters.