Many pre-Slim PlayStation 3 owners are experiencing error 8001050F on their consoles and it's preventing players from logging into the PlayStation Network plus improperly displaying or corrupting trophy data.
Sony has posted on their Twitter page stating that 120GB and 250GB Slim models are working correctly and they are looking into the situation. Users who have converged at the NeoGAF forums theorize the error is due to the PS3's internal clock having a leap year-related bug and are advising everyone to not use the console for at least 24 hours in the hope that the problem fixes itself.
We'll update when any significant developments arise. Definitely keep an eye on that Twitter page as well.
Update: Sony has made a post on their blog advising all pre-Slim owners to not use their console for 24 hours. The error can cause data loss that may not be recovered.
Update 2: As of 3:55pm PST, various sources around the internet are reporting PS3 units are functioning correctly again. Go and catch up on some playtime you missed.
Update 3: Sony has confirmed the issue is resolved as of 6:25pm PST.