I think Philly is pretty good. My commute is fantastic--1 mi on low-traffic streets, 8 mi on MUP, then 1.5 mi on some of the less busy city streets. There aren't throngs of commuters on the MUP, but there are several, and almost everyone expects and deals with bike traffic (i.e. only the occasional long leash or people obliviously strolling side by side to take up the whole path).

But I think it depends a lot where you are. My path is there because of the park along the river, so there aren't many other such paths. And bike lanes tend to be intermittent and often don't connect to each other. The commuters at my work are all from Mt. Airy and West Philly.

Cars do seem to at least know that there are things called bikes that sometimes use the roads.