Which now looks pretty much like this: "In a large swath of the East Side bounded by Fifth and Park Avenues and East 49th and 70th Streets, about 30 percent of the more than 5,000 apartments are routinely vacant more than 10 months a year because their owners or renters have permanent homes elsewhere, according to the Census Bureau’s latest American Community Survey."
http://www.nytimes.com/2011/07/07/nyregion/more-apartments-a...
Per the article, 5% of Manhattan apartments now have absentee owners who don't rent them out. And below 96th street that figure probably doubles.