Thanks Carmen, for the link! Is that the elusive St. Patrick's Day dress we see? Correction: Erin informs us "It’s not the same dress as the St. Patrick's Day. I was sitting in the orchestra and had a good view — this one had a fitted bodice with a tulip skirt of little tiled patches of the green fabric."
Update: We are delighted to discover this dress is another gem from Jason Wu! The green dress is from his Spring 2009 collection, seen here. Since this wasn't a widely photographed event, hopefully we'll see it again? Fingers crossed.