I recently worked on a depth effect without the need for 3D glasses.
Notice the enhanced depth between the people in the car (Jennifer Aniston and Gerard Butler) and the background. You should be able to see it with the van too as the guy fires the gun. The 4 to 6 second mark.
http://www.youtube.com/watch?v=rMSt0kSzBxs
When Butler says "the only person around here who wants to kill you is me" - you should see greater depth between him and Aniston, and Aniston and the background.
The effect doesn't seem so striking on certain films which is a shame because it's limited its potential. However, given the right film and some other technical details which I won't bore people with, I believe it's possible to create the illusion of extra depth within a 2D image.

That clip is probably the best example of the effect so if you can't see any difference, just lie and say "wow - look at that depth!"
I mantain that is greater depth, so I believe it's possible. I don't think I'm making it up!
But as I say, it doesn't work with every film and it's a subtle difference, it's hardly stuff coming out of the screen and touching you! Back to the drawing board...
The success of Avatar proves people will see films in 3D although I think the advanced CGI was the main reason for the film's success.