I was probably most upset when The King's Speech beat out The Social Network, because, while I really liked The King's Speech and thought it was a deserving nominee, I knew The Social Network would be the lasting film, the one the file under classic, whereas King's Speech would be filed under, "oh yea, that was a good movie".
But then I started to realize to not put any stock into who won awards, since, you know, film is art and art is subjective, which makes it a bit hypocritical to name a "Best" anything. So now I just watch awards as celebration and not competition.