Not sure how many are working on 5.1 mixes, but I was wandering around the internet and ran into Wendy Carlos of "Switched on Bach" fame. www.wendycarlos.com is really a great site. I ran into this essay on surround mixes and thought people might be interested. Some ideas on recording, too.
I also stumbled onto her site a while back and bookmarked it right away. She offers an in depth explanation of what surround sound is and the way it's supposed to work, along with the history of quadrophonic sound and her involvement in it. By the way, in the picture, notice the 4 Klipsch Cornwalls, not on the floor, but suspended from the ceiling. She was one of the early adopters of the original Moog synthesizer, which I believe you can see on the right in the same picture. You can easily get lost in that site. It's fascinating.