Like Pete D, the side speakers in my 7.1 setup are slightly ahead of the listening position. This helped fill the sound stage between my mains and surrounds, and this sounds to me more like a theater. I think the rear speakers help anchor the sounds behind you similar to how the center speaker anchors sound in the center. I really like the 7.1 setup because the sound staging stays fairly fixed even when you move to different places in the room. As JohnK points out, the PLIIx modes help anchor the rear sounds on the 5.1 sound tracks.

I second LOTR and Star Wars as great 6.1 movies.