I think deleted characters is partly what the OP is about but it leaves out a major factor that causes characters to delete. Turning your system off while any one of the spinning save/loading circles are spinning (or frozen).
I've only lost my character once (God... sad that sounds like an achievement) but when I did my game froze and I restarted after like 30 seconds. I think in this timeframe, there was some sort of communication with the servers that corrupted my data and hence my char was deleted. Almost EVERY person who I've talked to about their characters being deleted have shut their systems off in a hurry trying to get back in the game.
My safe solution, which has worked for me flawlessly so far when my system freezes (more of a theory than law since we can't actually confirm) is waiting 10 - 15 minutes before turning your system off. The logic behind this is whatever is going on in the background that got frozen, 10 -15 minutes is more than enough time for the cloud to resolve your character and timeout/drop the connection allowing you to reset your system appropriately
It is a painful wait.... but it's infinitely better than having your character deleted. Like I said, the OP touches on part of it, this is the other half and a part that a lot of people aren't heeding to. Remember that caution warning at the beginning of game load... please do not turn off power to your system when you see these symbols...
I lost my last character yesterday without my system freezing or anything.
I was playing, decided to stop playing, switched to single player, saved in single player and then turned off my PS3. Today it was gone.