I've got probably 10' behind my seating area (not a dedicated, sealed-off home theater room, but entertainment area) and I use the 7.1. I went that way because I was having the basement finished and figured that I might want to take advantage of the rears in the future, even if not now. I went ahead and put the wiring in and eventually caved and added the speakers, too. ALthough there's a very limited selection of movies for it, I figured that eventually it will become the standard, perhaps after HD disks become mainstream. It's also handy for listening to music now, since I can set the receiver to output from all 7 and get consistent sound through the room for parties and such.
Cheers,
Kevin