I found the following that other people felt were mistakes at the Oscars
Jim Carrey not even being nominated for The Truman Show
Back in the day, The Golden Globes were seen as a foreteller for the Oscars, at least as far as the nominations were concerned. And if you won a Golden Globe, it was pretty much a guarantee that you would get an Oscar nomination. Well, there were no guarantees in 1999 when Jim Carrey won a Golden Globe for Best Actor for his performance in The Truman Show, and then was snubbed by Oscar, not even getting nominated for marvelously playing the unsuspecting Truman Burbank
Memento loses screenplay award to Gosford Park
In terms of uniqueness and originality, the only movie since Being John Malkovich to achieve such greatness would have to be Christopher Nolan’s magnificent Memento. It’s backward zig-zag structure is incredibly daring, but effective and just wonderful. When Oscar came around in 2002, I had learned a few things from past Oscar’s, and I figured that the only nomination Memento would garner would be for its screenplay. I was actually wrong, since it was nominated for Best Editing as well, but you get the idea. I figured that since most of the big dogs for the year (In the Bedroom, Fellowship of the Ring, A Beautiful Mind) had their screenplays nominated in the Best Adapted Screenplay category, and Memento was nominated in the Best Original Screenplay category, I figured it was a sure thing to win. My jaw hit the floor when Gosford Park won. This, my frienRAB, is the biggest Oscar mistake, not just because Memento didn’t win, but also because Gosford Park was such an unbelievably crap-tacular movie! There’s a decent little twist at the end, but it’s primarily a bore-fest. The first hour is completely useless and it’s just plain, sloppy storytelling. There is no way in Hades that Gosford Park had a better screenplay than Memento. There’s just no way at all! Period!
Back in 2001 A Beautiful Mind beat The Lord of the Rings: The Fellowship of the Ring for best movie.
Alfred Hitchcock was nominated 6 times for best director but never ever won a oscar.