I live in Boulder, and ride around the area quite a bit.
I don't think any town is truly the "mecca" some people imagine that it is. On the other hand, often people who live in a nice area for biking don't see it for what it is, since they still focus on the few negatives.
Boulder is a pretty damn nice city for biking. Not perfect, but very good. I live 2 blocks from a grocery store (and if you live in boulder proper, it would be hard to be more than about 15 blocks from one), a liquor store, a laundromat, a bike shop, a coffee shop, etc. The city has pretty good bike lanes (but the old part of town usually doesn't have a shoulder, even on the arterials), and has a MUP system that is actually useful.
I commute to work, about 5 miles. I live on one side of town, and work on the other. There is a MUP path that goes along the Boulder Creek that gets me nearly all the way to work. Unlike the MUPs in many other cities I've lived in, this one is pretty bike-centric. I can haul-ass the whole way to work, and because it underpasses all the roads, I don't have to stop until I get to work. There are peds to watch out for, but they mostly stay to the side, and respond in a friendly way to my "on your lefts".
Most places have ample bike parking, but bike lockers are not common, except at the park and ride stations for the RTD bus system. Busses are pretty good, but honestly, I hardly ever take them. The exception is to the airport, it is much easier to bus to the airport than to try to drive.
Boulder is a college town, which is GOOD for cycling advocacy, lots of educated outdoorsy people, boulder has one of the highest college degree per capita rates in the whole country. It is also a transient town, and a party college, which is tough. The first time I've EVER been hit by a car was when I moved back to Boulder about a year ago, and got hit crossing the street, with the light, in a bike lane, covered in blinkies, by a guy with a .2 blood alcohol in a pickup. He drove off, and fortunately, was identified by a friendly passerby and caught by the police. I wasn't seriously injured, his insurance replaced my bike and he lost his license, but still, after 7 years of riding daily in St. Louis city, I didn't think Boulder would be the first place I got run down.
So anyway, I think Colorado in general is quite good for biking. I've lived and commuted in Boulder, Fort Collins and Denver, and of the three, I'd rank their "bike friendliness" like this:
* North Fort Collins (no-pro, to anyone living there)
* Boulder
* The rest of Fort Collins
* Downtown Denver
* The rest of Denver
That is a pretty simplified list, based on where I've lived and ridden, but its how I see it for the moment. There are still some things I'd like to see improved in all of these areas, but I think we've done a pretty good job, and I'm happy biking around every day.
-Sam