You will see on your game page, and when viewing games from your archive, that there as a new "light-blue" PGN button for games that are completed. This button opens a modal window that contains the PGN text.
Currently it only shows a very basic version of PGN (only player names and moves). Please let us know if you need more details added.
Will look into making it downloadable... there isn’t much difference between the PGN and the existing move list, but a PGN is a very specific text format to port games between systems. With time we will probably expand the PGN. We are not using its full feature set yet.
Personally,I don't really mind if it's downloadable or not, I just couldn't see the purpose of it. Though I'm sure it will come in useful if and when it can be ported.