- some files, e.g. saved games, may get corrupted.
- trophy information may not be synchronized correctly and new trophies may get lost.
- most (all?) games cannot be started at all; it doesn't matter whether these are online or single-player (offline) games.
- PSN cannot be accessed.
From software engineer's perspective I can only say: WOW, that's a nasty BUG. It's amazing what consequences such subtle bug can cause, but on the other hand it's kind of terrifying if you think of other hardware that could suffer from that kind of programming errors, such as planes...