After hundreds of "best movie of the year", dozens of "products which will revolutionize the industry" in computing, dozens of "indispensible and invaluable" roleplaying books, I think it's safe to say I have gained some kind of saving-throw bonus vs. Marketing, and I'm probably not the only one.
Why do you think "viral marketing" and in-movie product placement are so big now? Just splashing up a big sign or magazine ad saying what a wonderful product doesn't go very far, and big claims don't go very far either.
For RPG books, I make my own decision after browsing at my FLGS, although my initial interest is often stoked by previews online. An interesting excerpt is a lot more meaningful than any amount of cover-blurb.
For movies, I just assume all comedies have a few funny moments we see in the trailers, and the rest is vaguely amusing, and that all action movies have a few big scenes we see in the trailers, and some stuff that strings those scenes along (and maybe a few smaller scenes that didn't get covered). Unless it's a movie I'm already interested in, I won't go see it unless I hear from friends that's it's good or a reviewer I trust (in that I've already agreed with them many times before and we have similar tastes) likes it. Even then, I'm not too likely to go see a movie in the theaters (last movie I saw on the big screen was Episode III), I'd rather pay $20 to buy a DVD rather than pay $10 to watch it once.