paulo,
the current one on not allowing radio equipment in flight in passenger cabins.
Radiation from receivers has been a problem for many years. In 1939/40, the only receivers the Royal Navy had with adequate performance (B34) were removed from ships as quickly as they could be replaced by B28 receivers because of radiation.
During WW2, the Germans were misled about Coastal Command radar for some time by some RAF PoW's who told them that submarines were being detected by radiation from their radar detection receivers - which, of course, wasn't the case. As some radiation was detected when they looked for it, a whole new radar detection receiver got designed.
And as far as avionics EMC is concerned, one of the interesting ones these days is the Tornado, which is notoriously subject to EMC probelmm - don't fly one too near a broadcast station!
I'm not sure which European EMC standard a GPS receiver has to meet - if it's EN55013, then there's a definite potential problem. EN55022 isn't, I think, applicable. I'll have to ask a friend who does a lot of testing.