I did exactly as you said. I had a Sony 5.1 receiver. As I mentioned before, the center channel started acting up. I just used stereo sound for at least a year.
About a month ago, I got my money from uncle sam and my wife ok'd me to get a new receiver. So I bought a Yamaha RX-V1600, which is a 7.1 receiver. She also, ok'd me to buy some speakers so we could use the 7.1. As of right now, I don't think there are any DVD's out that are 7.1. (I definitely could be wrong, and if I am, someone please let me know. I would like to try them out.)
I think that when hd-dvd and blu-ray finally come out there will be some, but that just means more upgrades. I am able to use the 7.1, it just divides the rear signal up between the 4 speakers. I am still learning this new receiver (which is awesome by the way). I do like the 7.1, but it has been so long since I've had 5.1, I can't give you an idea of the big difference between them.