As New York's new law legalizing gay marriage went into effect Sunday, hundreds of couples said their vows and emerged from New York City's city hall to cheers from spectators grouped outside. State officials planned to marry all 823 couples, both gay and straight, who applied for licenses on Sunday. With 19.4 million residents, New York is the sixth and most-populous state to legalize gay marriage. Clerks' offices in New York City are typically closed on Sundays, but are open today to honor the law. Gov. Andrew Cuomo held a party in the city to celebrate, and Mayor Michael Bloomberg officiated the wedding of two of his aides.