I concur with the excellent ground performance of the Ipad2 GPS, but that is GSM assisted.
IME the airborne performance is rubbish and about the worst I have ever seen for any handheld device.
I am on my 2nd Ipad2 (the 1st one stopped working) so it isn't a duff unit - unless they have a bad batch.
Many things can affect GPS reception on a self contained handheld.