Interesting article I read last week, someone on Drone Chat just reminded me of it.
You can pick one of these up for about £30, and it could really ruin a day at the field.
I've not noticed any strange GPS behaviour yet, but after reading this article i feel a bit apprehensive every time I see a delivery van go down the road past my flying field.
However, there is also some good GPS news on the BBC at the moment.
10cm accuracy, even built up areas :D