Here in NYC, espeially in midtown, downtown Manhattan and parts of Brooklyn there is no need to be stealthy. Most People just don't care and/or assume you are a tourist. Of course, if you fashion yourself a ninja and want to snap shots of a paricular person you can be sneaky. In any case, generally people are just in a rush and don't pay attention.
I spend most of my time shooting in neighborhoods that are not so nice. Granted, I only photograph people probably 10-15% of the time, But I've found that being sneaky in these types of areas is NOT a good idea. It actually can be dangerous because you will be assumed to be an authority figure, or someone who may be trying to catch someone in the act of some real or imagined illicit activity. Anyway, I've found it's almost always better to be obvious and thus, you are pretty much telegraphing that you are not a threat. What I do is I find an interesting spot and I stand there for a while then begin taking photos once a comfor level is achieved. If I get bad vibes i move on. Using old cameras, like my mamiya c330 or hasselblad also helps as they are more obtrusive. Anyway just my personal experience 🙂