So there I was, working on some Windows Forms in VS 2003. Suddenly, like a bolt from the blue, VS decides that it's going to drop all the form elements from a panel within a panel that included a splitter and the custom datagrid I'd spent all morning working on. How happy was I...
Thankfully all the code still existed, so I just had to manually add the objects to the form at the end of the VS generated code.
Makes your heart jump into your throat when that sort of stuff happens...