At the retail store, they don't have refurbs in stock to give out.
So long as you have a stock config (i.e. you didn't order it online and customize it), if it's within 14 days of purchase, they'll almost always give you the option to swap out for a new one of the same config.
After 14 days, they'll usually have the Genius Bar repair any problems, although some folks have gotten swaps after the 14 day mark.