Yorkville, New York City - good neighborhood for singles?

No! Uptown, in general, is famous for being the area where downtowners move when they have a family. The bar scene is minimal and most of the people in Yorkville tend to be a bit older and more established. The Upper East Side is kind of a downer on the social scene sphere and Yorkville is not an exception to that. I would even live in the Upper West Side over anywhere in the Upper East. There is, quite frankly, nothing to do there.