Cameron at Overstated compiled a side-by-side comparison of San Francisco neighborhoods with their supposed cognates in NYC. (I thought Chelsea was the east coast's answer to the Castro, but what do I know?)
Check it out here. As to be expected, there's much discussion in the comments secton.
I've never lived in NYC, only visited many times, but I never ever thought of Union Square:SoHo, though. Yeah, you can shop in both places, but that's too easy a comparison. SoHo's more edgy and modern, reminding me of boutiques you'd find in Hayes Valley/the Mission/the Haight, even. But Union Square? For hustle-and-bustle and public transportation hub factor, I say Union Square:Times Square (minus the roasted nut carts in the winter - yum!).
Also, Staten Island's feeling a bit left out, although I've never been there to even venture to give my own opinion on it.
I guess Oakland's what ... Hoboken?
Don't hate on Oakland, yo. Seriously.
Cameron is right about one thing though: Jah help you find even a semi-decent burrito in NYC.
(Props to Overstated for soothing my Manhattanlust, as I had to postpone my NYC trip again.)