maybe people could make a post above warning people that the ending will be disscussed...or if you see the name of a movie you haven't seen yet just skip the post
Some forums have a feature that allows posters to cover all spoilers with a black bar. The individual reader then decides when to uncover it. It's a neat solution IMO.
I am a member of the Stephan King MB and they have a spoiler button. It works great but of course there are a whole lot more spoilers on that forum than this one but the idea is great.