We’ve been hearing about James Cameron’s “Avatar” for what seems like an eternity now. At nearly $300 million, it’s the most expensive movie ever made. Its marketing machine has been at full force for months. It has a spectacular trailer. And now the critics are getting in on the act.Roger Ebert has given it four stars and it’s doing well on Rotten Tomatoes. It’ll be the box-office best for its opening weekend (this post was written before the premiere).

Conversely, Transformers 2: Revenge of the Fallen was the 2009′s highest grossing film at more than $400 million domestically, yet it had a 19 percent approval rating from the critics on the Tomato meter. I didn’t plunk down the money to see it, and still haven’t, but what from I listen to most seriously — word of mouth — it’s the worst movie ever made.

Word of mouth is an interesting animal. When I saw the trailer for Sandra Bullock’s new based-on-a-true-story movie, “The Blind Side,” I laughed it off as a cheesy Disney I’m-a-rich-white-person-giving-a-black-kid-from-the-streets-a-chance tearjerker. It didn’t start at No. 1, and movies usually drop off dramatically after the first week, but it has to-date grossed more than $150 million. The reason? Word of mouth and social networking.

I haven’t seen it yet, and probably won’t in the theater, but I am definitely interested in checking it out after hearing good things from people I know. It’s funny how you can write something off because of bad marketing, a poor review or a cheesy trailer, yet will change your tune once someone you trust vouches for it.

'The Blind Side' was based on Michael Oher (center)