Didn't the major airports, like DCA, ORD, and JFK do some sort of open slot agreement w/ the government? That explains the new terminals at ORD and JFK. Also, check JFK again. It isn't as full as you say. Terminal 6 has plenty of space. I know because I was there Thursday(8-12-99). I think an airport is full when just about every gate at the airport is used up to capacity.
Some other things you should know about JetBlue:
-70% of their flights will leave between the morning hours and 3 pm. Between 3 pm and 9 pm is heavy transatlantic traffic so JetBlue is only using those times at a minimum.
No, JetBlue is not going trans-atlantic. The forum user was stating that between 3p.m. and 9p.m most slots at the airport are used for trans atlantic flights. Anyway, I think that the slot problem will be JetBlues achilles heal and ultimately cause their bankruptcy. I don't think the carrier will do that well.
"History does not long entrust the care of freedom to the weak or timid." D. Eisenhower
jetblue shouldn't have any trouble with slots at jfk. earlier comment that jfk is at capacity only a few hours each day is correct; it's just during the evening trans-atlantic rush hour. the rest of the day, jfk sits almost empty!