There are other legal channels available for this purpose other than 123.45. I would never use 123.45 in a formation for the aforementioned reasons as you never know who will be on it. Some of us use powerful radios that will receive and transmit for up to a couple of hundred miles, so 123.45 is usually completely out of the question.
If someone could post the other legal channels here that would come in handy; I don't have them on me right now.
I say bad luck if you are stupid enough to discuss company / private info over the airways on a "chat" channel. Everyone knows you are supposed to talk in code and add 100 knots to all of your airspeeds when comparing.
I remember one day cruising along discussing a porno we watched the night before when this voice cuts in and says "the two aircraft tracking south there is a Warrior coming straight towards you," then a quick evasive move to avoid him. Seems the guy with the handheld was listening to us for ages and when we flew overhead happened to notice an aircraft coming straight towards us. Felt quite lucky after as it would have been close. Some could argue that if we were on centre we would have been warned, but that's what the other radio's for.