Boulder is known as "The Peoples Republic of Boulder" or "Sixteen Square Miles Surrounded by Reality. All jokes aside, it's a really neat town. As far as getting to Colorado and getting to Boulder. I'd recommend coming into DEN instead of COS - you'll tack on at least an hour drive time each direction via the Springs. DEN is a pretty good, clean airport located just north east of Denver and about 45-60 odd minutes from Boulder with no traffic.
A lot of people do commute from Boulder and Denver and vice versa during the week. So the morning and evening rush hours can add a significant amount of drive time.
As others have mentioned, the Pearl street mall is a fun place and shop and Hippy watch. Lots of great restaurants in the general area. If you're into beer, there's Boulder Brewing Company, Avery, Southern Sun, Readstone Meadery in Boulder, and Oskar Blues, Left Hand, and New Belgium within an hours drive.
I'd suggest going up to Rocky Mountain National Park for a day if you have time.