For example, NYC has "fixed" the law to be very clear.
"What the Law Says -- Contrary to what many may think, New York laws about short term rentals are pretty clear, thanks to a new law went into affect in 2011. "Under the New York State multiple dwelling law, a residential multiple dwelling can only be used for what is termed 'permanent resident purposes,'" explains attorney Robert Braverman. "What that means under the statute is that it has to be occupied by the same person or family for 30 or more consecutive days." So anything less than 30 days, no matter how you swing it, is violating the law, unless of course, the place is zoned to be a hotel or hostel."[0]
"What the Law Says -- Contrary to what many may think, New York laws about short term rentals are pretty clear, thanks to a new law went into affect in 2011. "Under the New York State multiple dwelling law, a residential multiple dwelling can only be used for what is termed 'permanent resident purposes,'" explains attorney Robert Braverman. "What that means under the statute is that it has to be occupied by the same person or family for 30 or more consecutive days." So anything less than 30 days, no matter how you swing it, is violating the law, unless of course, the place is zoned to be a hotel or hostel."[0]
[0]: http://ny.curbed.com/archives/2013/03/25/an_introduction_to_...