Which Do You Prefer: 5.1 vs. 7.1 Surround Sound? - The current poll over on the AVS Forum addresses surround sound, with these configurations virtually an even split among the home theater enthusiasts.

[Electronic House]

As of right now in the poll, 5.1 and 7.1 are equally preferred.  Those that prefer 7.1 seem to have larger or unique rooms.  7.1 does require more current hardware, but there is very little 7.1 content available.