I've been using a wi-fi only ipad plus external bluetooth gps receiver plus foreflight since July and it works great.

I had to jailbreak my ipad to get the GPS to work.  I used Cydia to jailbreak the ipad, loaded BTStack to enable ipad bluetooth GPS devices, and purchased a MobileMate 886 Mini Bluetooth GPS receiver ($56 on amazon) that i set on the glareshield at the start of a flight.

I'm able to turn the ipad on and off in flight, and Foreflight immediately resumes as though i never turned the ipad off because the bluetooth GPS receiver stays locked on the satellites while I have the ipad turned off.  Does it work the same way on an ipad with its internal GPS?  In other words, can you turn the ipad off in flight, leave it off for 30 minutes, turn the ipad on and have an immediate GPS location?

Does the internal ipad GPS work just fine through a carbon fiber fuselage top, or do you have to position the ipad in some special way?