trailer trash talk

I'm preparing to run a focus group or two this spring on movie trailers, basic research designed to collect some evidence for subsequent work. One seemingly widely shared feeling about trailers is that, with all the economic pressure placed on opening weekend grosses, trailers often tell us too much about the movies they advertise, giving away plot developments and gags best experienced while watching the movie itself. Basically, the folks marketing the movie don't care whether they impoverish the experience of actually watching it, as long as people buy tickets. I'm also interested in the meteoric rise of trailers online, how that might be different than seeing them on television or in theaters. Have the new "red band" trailers for R-rated movies made any difference in what movies people see or why? Open to suggestions here, let me know what you think, thanks.