Ah the Peoples Republic of Boulder...
Crime is much less than say Denver which I find is a safe enough town. It is a high density area for sure, and the city council and others who run the town, seem to have to find stuff to regulate all the time to justify their jobs. That gets a bit annoying. World class rockclimbing, hiking, mountain biking, good kayaking, and other things to do right out your door.
Most of the crime related to college type activities. Drinkin', drugs, occasional brawls, etc. Be smart and I doubt you'll have a problem. Tons and I mean tons of hot girls there. I love going climbing in Boulder when the school is getting ready to start in the fall.