Outlawed by the state in 1975, an exception for their use in NYC was granted after a 1990 lawsuit. Starting in 1992, and continuing for the next 16 years, the city repeatedly tried and failed to move beyond the testing phase of various toilet proposals. By 1994, after a mere two years, the NY Times was already fed up:
"The city's frustrated attempts to meet the basic human need for a safe, clean place to go to the bathroom exemplify how cumbersome governmental processes, flawed planning and a cacophony of competing interest groups can delay the achievement of a common-sense goal."
Finally, in 2008, it was all figured out. The first post-1975 permanent pay toilet was installed in Madison Square Park to much fanfare, with the promise that 19 more would soon be in place around the five boroughs. (Here's a review of that toilet, for those curious about the workings of an automated commode.)
However, by late 2010, there had only been one additional toilet installed (in Corona Plaza, Queens). But after more than a year of wrangling, work was finally underway on a third location, here at Grand Army Plaza in Brooklyn.
So now it's 2012, and we have a grand total of three pay toilets to show for two decades of bureaucratic maneuverings. (I assume there are still only three: the city's own website lists just the first two.)
Finally, it should be noted that these machines consume a monstrous 14 gallons of water per use! Perhaps it's for the best that they remain so few and far between.