I do about 20mins/mile with a few bursts: fun part is avoiding tourists, or smokers. :)
The tourists look like they're in a trance, looking up, starry-eyed jaw agape. I can understand the awe, but I wish they'd come out outside of rush hour instead, especially when there's a family of four, holding hands or walking slowly should to shoulder, and sometimes they even drag luggage behind them. The most idiotic thing I've seen is for them to take pictures of stores. Mind you, not rare stores, but just generic stores, or fast food restaurants/coffee places. Are McD's or Starbucks really that rare everywhere else in the world?
Smokers are the most annoying, especially if they're ahead of you. I'm sure diesel exhaust is probably worse than cigarette smoke, but it doesn't make it any less annoying when there's a pool of smoke in front of you and you have to hold your breath while you rush past one smoker, only to find you're now behind yet another one. Even more annoying are smokers who go to Central Park and smoke, yeah, how nice that you've come out to see and enjoy nature and pollute it. Thanks buddy...
I find that walking on the edge of the sidewalk is the best way to do that. There's usually obstacles, such as newstands, hydrants, flowerpots/metal posts, people handing out flyers - some holding very large wide signs so as to use up even more space, etc., so I almost always switch to the street gutter and quickly get around them, but now there's pedicabs to avoid as well.
After 9/11 they put big flowerpots in front of a lot of buildings, or just metal posts, I guess they're worried about someone driving a truck into a building or something, but it makes the sidewalks much narrower, so more congested. There's also a lot of construction these days with closed sidewalks/scaffolding.
So NYC's a big obstacle course if you're walking. It's probably worse if you're driving or biking.