It's not finished yet, but some segments of the First Avenue bike lane are quite rideable. I used about eight blocks of it this weekend.
This Saturday, I was able to bike from my apartment in Prospect Heights to the East Village, and back again, without really leaving a marked bicycle path. The only exceptions were the side streets at each end of the trip, and those felt a million times safer than crossing high-speed traffic sewers like Atlantic Avenue and Houston Street.
A lot of the bike infrastructure on that trip -- including the Allen Street lane, the Sands Street bikeway, and the brand new Vanderbilt Avenue bike lane -- didn't exist a year and a half ago. The protected lanes on First and Second are creating some extremely useful connections to these recent improvements. You can ride for long stretches and feel like you're using the genuine article: a safe, connected bike network.
Living where I do, I'm lucky enough to be able to take advantage. New Yorkers who live in East Harlem and on the Upper East Side deserve an ironclad guarantee that they'll get access to this network of safer streets  as soon as possible.