Arne from Naughty Dog writes:
"Recently, we've been monitoring an issue in the "Ranked" playlist where players are seeing their playlist-specific skill rank being reset to level 1 throughout the course of play. In order to resolve this issue, we'll be resetting the skill ranks for all players within the "Ranked" playlist on Friday, January 15, 2009 at 12:00 PM PST (what time is that in my city?). We will also be letting everyone know through an update of the multiplayer Message of the Day at that time.
Now don't panic! We're NOT resetting your overall progress or any other part of your accumulated stats. Your skill rank ONLY exists in the Ranked playlist and it is the number displayed between your level and your PSN ID – your level and the cash you've accumulated to date won't change at all."