For most New Yorkers, a chance to have a cocktail on one of the private roof gardens of Rockefeller Center is reason enough to head to a party, but add in some of Hollywood’s most stylish stars and a jaw-dropping collection of diamonds from Piaget, and you have an invitation that the fashion elite simply couldn’t say no to. While Leighton Meester and Emmy Rossum, both in strapless dresses, chatted excitedly on what part of the roofdeck, Liv Tyler and Maggie Gyllenhaal found a quiet place to sit and chat. And besides the glittering jewels and the amazing views of St. Patrick’s Cathedral, the buzz of the night was how slim and gorgeous both Tyler and Gyllenhaal looked. Liv told PEOPLE that she can’t credit exercise with her slim figure, “I’d like to work out, I’d like to do exercise, it would be good for me, but. . .” Whatever she’s doing or not doing, she certainly looked as flawless in her Oscar de la Renta dress as the diamonds in the featured Limelight Paris-New York collection.