Interestingly, Denker
says that "many airliners .... that do have fancy angle-of-attack sensors don't make the information available to the flight crew — only to the autopilot". That suggests to me that an AoA-instrument doesn't give you very much in the way of useful information.
Oh, and my PA-28 seems to be very good at telling me how close I am to the criticical AoA without any instruments at all - you get a very noticable pre-stall buffet through the yoke. Admittedly the stall itself is a non-event, but you know it's coming.
I guess the washout in the PA-28 wing means that an AoA indicator is meaningless, anyway?
(edit: just noticed a rather odd spelling of critical
)