Nothing wrong with living near the UN. 51st is 9 blocks north of the UN, anyway.

I lived on 52nd between 1st and 2nd as a baby (1981-84), and my parents loved the neighborhood because we could walk to everything in Midtown...Grand Central, 5th Avenue shopping, theaters across town, even Madison Square Garden if we were up for it. Subways are relatively close, too---the 6, E, and V stop at 51st and Lexington, at the Citicorp Center.

It can get a little pricey, even by Manhattan standards, in the east 50s so if you find a good deal go for it!