In my 5.5 mile usual route to work in Chicago, I have something like 30 stop signs and 25 lights. So, 4-5 lights and 5-6 stop signs per mile. If I go another mile to a different office, you can probably tack on another 6 or 7 lights. I slow down for everything (unless there's a clear line of sight and clear traffic, which is usually a few of the lights and probably half of the stop signs at least), come to a stop when I have to, stay stopped if I feel like it.

Probably once every 3 weeks the gods of timing are smiling on me and I can make it home without coming to a complete stop. I am not someone who enjoys challenging cars to dodge me while I run red lights, but I am also reasonably impatient and usually in a hurry to either eat something, drink something, or pick up another package of bike crap before the post office or UPS store closes. On the way to work I'm in much less of a rush, and will totally come to a stop at a red light with little cross traffic. The office isn't going anywhere, ya know.