Ok, I was half right! While it is an official frequency for A2A for pilots in oceanic regions. "VHF inter-pilot
air-to-air frequency 123.45" and per reference to ICAO, it is also a A2A frequency for oceanic routes where HF communication is lost. As I read more, 131.8 was replaced by 123.45 in Oceanic regions.
I guess I was wrong though! The "official FCC" (yes, not issued by FAA) one is 122.75, I found this in the AIM TBL (table) 4-1-3.
Anyways, sorry for my mistake! Now that I see that, it is a very misused frequency. I have heard everything on it, from friends here in formation, to airliners, to parachute jumping, to many other kinds of operations! It's official to us pilots, let's go with that!
I'd say there is more that use on 123.45 versus 122.75.