Intended to solve some of the GPS problems of the iPhone:
GNS 5870 MFI GPS Bluetooth Receiver for iPad
Reviewed in Flyer last month, I think.
I'm thinking seriously about this sort of solution as I need to replace my Lowrance Airmap 1000 due to the stupid decision by Lowrance no longer to provide database updates. I already have an iPhone and am thinking of an iPad anyway, so the GPS addon might be all I need to get a working solution.
Tim