I'm out in the suburbs of a large city so congestion is not really a problem unless you're riding with the flow of traffic in the morning between 7-9 AM and 3-7 PM. Even then it's not so bad. I went out early this morning against the flow, not that it mattered at 6AM, and my first stop light was at about 30 minutes, and then perhaps every ten minutes or so there'd be another light.

I've also ridden in that big city during rush hour and it's exactly as the OP described. Not only that, but there are a ton more parked cars, so the probability of being doored is high, and the corridors and roads are just that much more narrow. It's not a pleasant experience.

The trails in the city aren't much relief for congestion either, with all the commuter cyclists, children, skaters, walkers, runners, etc.. So if you ride during those busy times pick your poison.