I have had one for about 5 years. It's strange because, when I first got it, I had the best sleep I've ever had in my life. That wore off after a couple of months, though. Not sure why.
Over time, it became more and more difficult to find a good sleep number for myself.
I've since bought a gel-infused memory foam mattress and really like it.
The big advantage to the sleep number bed is if you regularly sleep with somebody else who has a different sleep style than you. I like a little softer mattress, my ex liked very firm. It worked well for us for that reason.