Here is my "definite" answer (I'm kidding):
I have my surround speakers a bit above ear level, so as not to block the sound for my wife sitting next to me and vice versa as mentioned by jautor. I have them tilted and pointed at us as the on-axis performance of loudspeakers is normally better than the off-axis performance.
If it were for me alone, I'd have them at ear level.
If you listen to classical music, the good surround mixes are incorporating the surrounds more and more directly with a sound stage of 180 degrees rather than "ambience sound"
If you have your surrounds next to you, a recording like Mahler's 9th ( http://www.amazon.com/Mahler-Symphony-Claudio-Jugendorchester-Accademia/dp/B0009JVOIO/ref=cm_cr-mr-img
) will put you in the virtual position of the conductor with a 180 degree sound field. If you move back a bit, it will sound as if you are in the center of row 1. That's what I call "surround sound" and it puts a smile on my face every time.
Of course, your speakers need to be positioned right, you need to deal with the reflections and they need to be balanced for loudness, as Ethan points out.
If you listen to "Master and Commander" in the opening scene, you hear the moaning and squeaking of the ship all around you and it feels like you are on that ship.
Now not all movies or concerts are recorded that good, but for the ones that are, you can't beat loudspeakers pointing at you and the movies will sound a lot better at home than they do in the cinema, imho. And I don't think the not so well recorded mixes will sound better by listening to them off-axis.