Hi,
>>I have found the GPS to be of crap reliability in flight (superb on the ground, when moving slowly) but it works OK with the XGPS150 bluetooth unit (another gadget to keep charged, so I don't bother with it).<<
Having just completed Oshkosh and back in a TB20 with an iPad 2 64gb 3G (mounted on the right hand panel) without an external GPS I can tell you that for some 9,200 miles the internal GPS never failed once.
We were running ForeFlight west of Iceland for the Canadain and USA IFR/VFR charts, plates and approaches and SkyDemon east of Iceland without a single problem.
Aero weather worked well for METAR's and TAF's
All in all using the iPad in the cockpit made life a awful lot easier.