Check out this article from the New York Times about underground construction in the city.
“Every weekday, 1.3 million passengers — more than are carried in 24 hours by the transit systems of Boston, Chicago and San Francisco combined — cram onto the Lexington Avenue line.”
I usually really like the subway — you can get anywhere in the city (five boroughs) for $2.25 if you pay per ride, which is pretty great compared to other major cities. I buy an unlimited 30-day pass for one-third of my transportation costs in Charlotte. No more gas, car insurance, or car payments! So while it can be cramped, especially during rush hour, the subway really is pretty effective for getting around town. You just really get to know your neighbors ;-).