It all depends i guess.
I recently picked up a Denon AVR-3805, which has 7.1, and i only use 5.1
Then again, it is probably because when i renovated the livingroom i only included runs for 2 surround speakers. I coulda gone 7, but the surround backs woulda been right in the back of my dome. It is not a small room, but the rear wall is right behind the couch. makes 7.1 kinda distracting.
The good thing is that the AVR 3805 sports 3 zones, it can do 5.1 DTS in one room, power another set of all weather speakers from whatever source out in the backyard, and i can run a cheap pre-amp/amp setup for the garage.
Personally i really like the way 6.1 and 7.1 sounds, there are good enough 7 channel logic programs that will go a good job of turning any 5.1 source into a 6.1 or 7.1
In my case, i just dont have room for all those damn speakers in my livingroom