I saw this short clip once with 3d glasses, it was in space.
You could REALLY see difference between visible planets (closer) and the stars as a background.
The stars were probably 2d though, since it was ~infinitely far away.
Caused a nice effect though, it was subtle, and very nice to see.
But for action movies and such, I wouldn't recommend it. It's a nice little touch which doesn't really work.