I've see people say stuff like "Who even remembers..." and then following it with Slumdog or Milk, but to be honest, outside of the fandom i still hear about them now and then, so yes, they left their mark and are still remembered. About Curious Case of Benjamin Button, it's another case of older fans of David Fincher not liking it much, but i remember the public enjoying it quite a lot, now if it deserved the nom or not is a completely different subject, i never watched Forrest Gump and it's been half a decade since i've seen Curious case, i was also around 13 when i watched it, but i do remember enjoying quite a lot.
Either way, snubs at the oscars are quite common, and as much as i love The Dark Knight, that one's not even the biggest deal of them all.
That said, Zack Snyder hasn't shown any of the brilliance that would make me think he deserves any kind of Nomination besides effects and sound, he tries to give a deep and complex plot and deal with major themes, but he lacks subtlety or patience to make things flow.