The "flying club" limitation, as far as I know, is a UK-specific limitation. I have never heard of this anywhere else. I'd be happy (not really) to be proven wrong though - anyone knows anything?
How does this limitation apply?
Does it apply to a pilot with a non-UK license, say, EASA PPL from Germany who is flying in UK and cost sharing after having invited some friends on Facebook?
Does it apply to a pilot with a UK CAA-issued EASA PPL who is flying in, say, Germany and cost sharing after having invited some friends on Facebook?
Can Facebook actually be considered public? Only the pilot's friends can see the invitation - it's as if he'd phoned them all and asked them if they wanted to join, isn't it?