All you have to do is just plop down your sleeping bag on the sidewalk next to a busy subway stop, snuggle up comfortably inside, and take a mid-afternoon siesta. What's even more amazing is that there are hundreds of people assembled only one block away yelling and screaming all day long to protest against the President of Iran, Mahmoud Ahmadinejad who is staying at the Warwick Hotel this week. Did I also mention the dozens of heavily armed policemen stationed outside the hotel as well?
If these sorts of things don't bother you then you have what it takes to be an urban camper. You'll also quickly learn to ignore things like taxi cab exhaust, curbside trash, cigarette smokers, and the thousands of people that trample by your camp site as they walk on by in Midtown Manhattan on a typical Monday afternoon.