I have found bluetooth physical link layer links to be more than reliable. I don't have extensive experience of BT in cockpit but the times I have it worked flawlessly. No noted interference either way (BT with radios, txpondr, intercom and other electrical).
Where problems arise is with the interface and application software. It is nearly impossible to validate all combinations of BT equipment with specialised software.
For example, one of my pet peves is the NMEA data emitted from GPS receivers, NMEA is a poorly specified and implemented interface standard and can cause less than well crafted interface code to crash. If this happens with a bluetooth GPS - it is more likely not the fault of the bluetooth layer - yet without knowing the exact cause we simply throw the baby out with the bathwater.
There are some really good Bluetooth GPS around but often these will not work well with just any target application code:
http://www.gpspassion.com/forumsen/t...TOPIC_ID=81990
I do suggest sticking with a Vendor endorsed combination of software/hardware and BT device.
BTW TCP/IP can happily run over a BT physical layer.
Doug