One problem with the early showings is all the little kids. If constant chatter doesnt bother you then its not an issue I guess. I wont see a movie I actually care about before 10pm. Especially if its the first week of a popular movie. Also, the more expensive the ticket (IMAX 3D, RPX, etc.) the less likely the theater will be filled with parents who couldnt afford a babysitter. I actually prefer 2D in most cases, but at least in Boston the 2D rooms in the multiplexes (the arthouses are different of course) are to be avoided like the plague.
Im sypathetic to those who can't afford a 20 dollar ticket or a babysitter for their 3-5 children, but Im not willing to suffer along with them. I only see a handful of movies every year, and even fewer in IMAX or 3D, so I have no problem paying a premium to see TASM or TA or TDKR in an optimum setting.