The one guy who worked at Mattress World seemed to know his stuff or he was very good at faking it. He explained all the numbers and terms to us, and what they mean for our "comfort."
They have a very nice floor selection, and they pretty much only deal in mattresses. My wife and I were generally surprised by the cost of mattresses. We shopped around many locations. Often we found better prices for lower quality items as well as used items, but in the end we felt it was better to compromise between price and risk and went with a middle of the line mattress. We sleep well on it, and we have yet to call in with any problems.