If so, have you ever noticed it's always the really good stuff that you lose when this happens?
Case in point: I actually started on a new manuscript, which is tangentally related to the one I'm revising. And what I was writing was really strong. I both developed the character in a really profound way, as well as had this complete catharsis emotion coming out. But then--blackness. Yup. My laptop totally died on me. Worse, I thought MS Word was set to autosave, but it wasn't, so the entire thing was lost.
But yeah, anyone else have stuff like that happen to them, and isn't it just incredibly frustrating?