Very still and quiet at ours, as well.
Lots of gasps throughout the movie. We took our 12 year old daughter with us. We didn't want her to see it with anyone else, in case she had questions, but like her big brother she really liked Chris Kyle and thoroughly enjoys this genre of film (gets that from me, I suppose). She said you could tell who read the book and who hadn't (she had...a requirement before going to see it) by the gasps from the audience at certain parts.
I asked her later what she thought of it and she said it was a good movie. Echoing The Monk, she is concerned that the Hollywood portrayal of all veterans having PTSD is what people who have no connections to the military will take away from the movies. Smart girl, that one.
No standing or saluting or anything like that.