FAA and JAA
If you have an FAA licence with a rating on it, you can fly that N-reg aircraft anywhere in the world.
The confusing bit is this - in theory you can fly N-reg aircraft in a country with a validation system based on JAA licence and rules, but only in that country.
Ie, if you have a JAA licence with a Isle Man validation for a GV, then you could fly an N-reg GV in the Isle of Man only, as long as you don't leave it's territory and you have approval from the authority.
Never used it, don't even know if it is correct, however this is what the FAA told me.
This leads to something else - if it is the case, does that mean I could fly and N-reg GV on my JAA licence in all of Europe (as it is a common licence to all countries), as long as I had the GV on my JAA licence, and I didn't leave the territory of a common JAA licence JAR area (effectively all of mainland Europe)?