No Canadians yet? Well, allow me to contribute...

I live in Calgary, Alberta. It's just north of Montana. The weather here is very similar to what Denver gets, but with much less snow. Calgary is all about sprawl. It's about 50km to drive from one end of the city to the other, and that's a pretty straight route. Still we have barely a million people here. Everyone drives at least part of the way to work, and that's where I encounter them. My commute is 100% on-road, but it's not dicey until I get about 4 blocks from work. Most people are pretty corteous, although I think that has more to do with me dressing like a messenger than anything else [shants + SS FTW]. The thought of me scratching the paint on their new Hummer or BMW keeps them away from me. I worry about bus drivers and worrk trucks a lot more - they don't care what they hit.

There is a somewhat extensive MUP system, but it is frighteningly narrow most of the time. I think it's 8' wide, with two-way traffic. The official speed limit is 20 km/h [12 mph], but I can easily get to 40 km/h on a road bike [as can many other people]. With hairpin turns, blind corners and some dicey bits by the zoo [they find the occasional body down there, and a homeless guy ate an eagle or condor or something that escaped from its pen], it can be very interesting to use it to commute. I avoid it like the plague, favouring regular streets. You have to keep a sharp lookout in the 'burbs [80% of the city], as it's really easy to get mowed down by minivans and SUVs.