Occasionally my client will completely freeze, and I have to CTRL ALT DEL to minimize the game (ALT TAB won't do anything). There's a popup saying 'DayZ is not responding' with the only option being to close the application waiting for me. When logging back in, my character at the start screen is in starter gear again, and logging in to a server shows that my character was indeed deleted. This has happened to me probably around ten times since release, through both of the patches released so far. I've seen similar reports on the official forums.
In addition, I have lost characters for seemingly no reason at all (no freeze). After exiting a play session normally and being sent back to the start screen, I see my character back in starter gear again. This is rarer, having happened to me personally only about three times or so.