There has been alot of migration in the "hipster" and artsy/creative fields from NYC - especially Brooklyn - to Philly, specifically Fishtown/Kensington and Northern Liberties. I stayed in a recently-renovated Fishtown rowhouse with a Haitian-American and Jewish couple from Fort Greene, and they had said many of their friends similarly made the move. Of course, these are people knee-deep in the art game, with actual projects, showings and portfolios, and are not the transplant wannabe's moving to Brooklyn because it's "cool", or what they see on Girls. Obviously, there is more to it, but this fits within the whole "more space for less" narrative that so often characterizes artist movement and transience. Through-the-roof real estate costs and COL have sent lots of NYC artists to Philly, Portland, Baltimore, Berlin, Detroit, or even deeper into Brooklyn.
Not buying into the silly, patronizing and borderline insulting "Sixth Borough" bs the NYT gave us a while ago, but this piece from a popular Philly blog makes mention of several trendy Brooklyn establishments opening up shop in Philly: http://nakedphilly.com/fishtown/fran...fore-our-eyes/
Also, those Dominican bodegas with "Philly Cheese Steaks"? More often than not, those people have relocated from, or have ties to, NYC (in this case, Washington Heights, Inwood, and the West Bronx-adjacent communities across the Harlem River from them). Lots of the Chinese have roots in NYC, too, and they are often frequent patrons of the infamous Chinatown buses that run/ran between the cities' Chinatowns. However, I wouldn't go as far as saying they all come from NYC, even if the connection is clearly there.