Depends. If there's an available trail/sidewalk and they're not using it, they're morons. I can't speak for everywhere, but where I live even riding in the breakdown lane will increase your chances of death by a few orders of magnitude. Fortunately there are enough trails to compensate.
As for the rules of the road:
1. I will gladly ride through vacant 4 way stops. They're vacant. If you're behind me, do you really want me to come to a "full and complete stop"? Not only would it break my rhythm, I'd think it would piss you off even more.
2. I use sidewalks based on practicality. In my area, the sidewalks are typically free (can't say the same for my college town, but it's legal there and there's no other option within the town for cyclists). If someone is in my way, I will go around them assuming it is safe (and alert them when I'm about 20 ft away). That may/may not include going on the road, going up an embankment, etc. Otherwise I'll slow and follow at a safe distance until a safe passing opportunity presents itself.
3. Crosswalks are for everyone, and you'll be sitting still or going about your business while I cross. What's wrong with my using them?