Well since the New Yorkers assume everyone knows what "Island" everyone will be at on Labor Day weekend I did my own research into it. It appears that there is a popular Horse Show in the Hamptons that week that draws a lot of celebrities. Looking at Google maps it appears Hamptons is on Long Island (though it is not explicited marked as "Long Island" but it is long). Not sure most are interested in Horse Shows nor determining what Manhattan club they attend based on whether there are celebrities there or not.