I was just talking with one of my developers (Alexey) and he said, why not just use Pg. Which is an interesting point. Consider that Volkswagen is properly known as Volkswagen but commonly (and most of the time) referred to as VW.
Why don't we just stop this whole PostgreSQL->Postgres->Postgre junk and just say, PostgreSQL, also referred to as PG.
Heck, I know plenty of people that just say PG, or PGSQL, myself included.
An issue with PG (or Pg) is that it is used for other things with about 170m Google hits.
One use of PG is as an abbreviation of Proctor & Gamble, a Fortune 25 company at pg.com and the PG stock symbol. Coincidentally, they are one of the big practitioners of brand management.
Would this be similar to naming a software project GM, a la General Motors?