I've been researching these and other beds the past two years. We've purchased three mattresses in the past five years as I've been trying to find one that doesn't hurt my back. With regard to Select Comfort beds, here's what I learned:
1) QVC sells the Select Comfort mattresses a lot cheaper than the storefronts do.
2) Comfortaire mattresses are a great alternative to Select Comfort. They're half the cost and made of the same material. I have one now and find them to be very good beds. Here's an epinions review
Epinions.com - Compare Prices and Read Reviews on Comfortaire Cerulean Mattress at Epinions.com
Also unlike Select Comfort, Comfortaire also has favorable BBB ratings - which is what won me over.