An interesting thread indeed.
We regularly use the Garmin GPS II+ in our training aircraft to track where a student has been on a navigation exercise ,(very handy debriefing tool when displayed track can be shown on a computer screen) with no effect on aircraft performance or systems.
These aircraft arent cessnas or the like, but turbo prop jobs with engine management computers and electronic flight display sytems. The GPS is attached by velcro over the intrument panel, so is nice and close to lots of wiring and instruments.
After all that, just because nothing has not happened to date doesn't mean that something can't go wrong. Remember that Murphy's law still applies.
If one wishes to use electronic equipment, be it a GPS or Scanner or so on, ask for permission to use it. At the very least all that can happen is that the answer will be, "Sorry No". If you are permitted to use your gear, and something unusual occurs, then the Crew will at least have a starting point to isolate the problem.
On a side note, The GPS II+ still works fine at 320 Kts, not bad for something designed for a 4WD (and not many can go that quick)