Only the people involved know the true story, for real... but man was this one hell of a cinematic experience. As with many films, characters are oversimplified for dramatic effect, trying to set the stage for a classic, epic battle between good and evil - in this case set on the (ultra) modern stage.
How much of it is true is certainly a question. But this was a very well made film. The power of Facebook and it's true pervasiveness in our modern lives is undeniable. This is a truly legendary idea, and to get a chance to even see the (even fictionalized) versions of these larger-than-life characters battle out the story was really inspiring. Facebook truly is a life-altering experience for so many of the users, and to see an "origin story" if you will, was really very cool.
The music by Trent Reznor was a strange, perfect fit and the pacing and script was top-notch. The part that was filmed in Tilt-Shift was mind-blowing. Seriously excellent job on the film. I hope at least some of the Facebook founders can enjoy it for what it is, rather than taking it for complete face value. The fact that they were (or are still) a part of such an epic story is truly inspiring. I think the public knows that there are a lot of grey areas in the film that were not truthful, not completely correct, or even complete fabrications for dramatic effect. I don't think it's meant to be a documentary, it's meant to be a twisting tale of epic proportions - where the "character" takes on more importance in the film than the truth.
Great movie, this is gonna win some Oscars for certain. Founders of Facebook: you've created a platform for the world to communicate and share their lives on, and that's certainty one hell of an accomplishment.