I used the AirTrain for the first time last week, to connect from the BA terminal to the DL terminal, and I thought it was awesome compared to the interterminal bus. The walk to the train from the terminal is very short, so even with luggage it is not that big of a deal. I just missed a train as I got off the elevator, but only had to wait about 90 seconds for another train to arrive. The whole process could not have been easier.

I'm pretty sure that I will use the AirTrain next time I have to go from JFK to Manhattan, connecting to either the LIRR or the E train (my NY office is at 53rd and 3rd, first Manhattan stop on the E train). It may not save a lot (or any) time vs. a taxi, but for me it would be a lot more relaxing. I totally stress out sitting in the traffic on the Van Wyck. (When I was in London last week, I took the LHR Express to the tube for the same reason; it saved no time, but it was much more relaxing.)