Yea, I forget the name of the shuttle service, but you pay 1 price at the airport (I think $20 or something, it wasn't bad), and you get a ticket for the shuttle to drop you off, and then pick you up and bring you back to the airport. For me, I got picked up around 2:30am when the 1up closed, and went straight to the airport for an early flight last year. So yea I think the shuttle runs at all hours...and they'll pick you up from pretty much anywhere.
Mitch I think you may be out of luck for rooms...or at least no more rooms at a discounted rate. The football game and other events that weekend made for a much busier downtown Denver weekend this year, I believe.