If you're trying to get some work done in Manhattan, give up trying to find a cafe with a seat, and hit the Rose Reading Room at the NYPL. Free wifi, lots of outlets, and it's freakin dramatically gorgeous.
My two complaints about Copley BPL is that they don't have nearly enough outlets for laptops, and their WiFi can be spotty in places. Of course, maybe Bates Hall will solve all those problems... ;)
They're good with the homeless too. Security guards walk all over that place constantly and wake anyone up who's sleeping. The bathrooms though, arg, across the street to Starbucks please. :)
EDIT: Ah man. It closes at 6pm alot of the nights. I usually like working later than that.
You can usually identify them by very generic terminology about internet business and (seriously, every one of them) a paper planner.
Makes me think of the beginning of Ghostbusters (although IIRC that was Columbia's library).