I have had a Select Comfort King size bed with all the bells and whistles (dual chambers, vibrate massage, adjustable frame, etc) It was great for the first 3-5 months - then it seemed I needed to change the firmness very frequently to be comfortable - that helped for around a year, then after that, I just can't spend allot of time on it.
I had back surgery and have a failed lumbar fusion so support while sleeping is very important. I have a military cot with a 3" memory foam pad on it that I find more comfortable. When I sleep on it, my chiropractor and massage therapist always comment...