Anyways, if you buy it in game - it would have to have been sold at a station, and the system is set up that you can't take PLEX outside of a station (or at least thats how it was about 3 months ago).
A recent patch a few weeks ago opened up the ability for PLEX to be transported by ship. CCP thought that would be a good idea to allow players more control of their items and I would have to agree with them. It's helpful for those who live deep out in 0.0 and would rather buy PLEX from a corp-mate than have to travel back into the Empire systems.
We are each entitled to our own opinion, but no one is entitled to his own facts. -- Patrick Moynihan