Regular cinema goers make their future movie decisions based on trailers, reviews, advertising and word of mouth?
It's 90% word of mouth anymore. Reviews and advertising count for nothing. Trailers just get their attention - which is a crucial factor to jump starting the word of mouth but can't carry financial success past the first weekend. That's when word of mouth takes over.
I would actually argue that it's the opposite.....that word of mouth probably counts for *less* than it used to, since movies are now so frontloaded and make such a large fraction of their $ early in their run, before word of mouth has a chance to kick in. Every single one of the top 10 grossing movies of 2008 made at least 25% of their total box office just in their opening weekends (that is, in just their first three days of release)......some of them a fair amount more than 25%.
Movies like, say, "The Sixth Sense" and "There's Something About Mary" (both of which are only about 10 years old), which have modest opening weekends but earn big bucks in the long run because of great word of mouth, are *way* less common than they used to be.
EDIT: By the way, "success" in the eyes of the studio does actually involve word of mouth in a way that's somewhat separate from the total box office numbers. If a movie earns $200 million by having a gigantic opening weekend of, say, $90 million or something, but then drops fast, as bad word of mouth spreads, then that's seen as being a much worse outcome than if the movie opened to only $40 million, but finally made its way to $200 million because of good word of mouth. In the latter case, the studio might conclude that the audience was still building, and people who saw the movie liked it, and so there would be a big audience available for a sequel. While in the former case, they'd be thinking that no one's really interested in seeing another movie in this franchise.
That's pretty much what happened with the Eric Bana Hulk movie. It had a huge opening, but then dropped fast because of bad wom. Even though the final box office tally was a big number, the bad wom convinced the studio that there wasn't the audience there for a straight sequel, so the only thing to do was to reboot the franchise completely.