Just had VS.NET exit without any crash message or anything. I was doing some editing and using the Tab key after typing part of a function name. I noticed that was causing a lot of disk activity a few times in a row, and then when I hit Tab VS.NET just disappeared.
I wish I had more information on this, but that's about all I know. I wasn't doing anything else unusual, just using some autocompletion.
A bit of good news to go with the bad news: After I restarted VS.NET and reloaded my project, VA-X advised me that a file hadn't been saved properly. I don't remember exactly how the dialog was worded (it did seem a bit confusing!) but the default Yes button brought back the file I'd just been working on, so I didn't lose any of my edits.
Try also to remove the NCB files associated with your projects. They can get corrupted easily and crash the IDE. This happens with or without setting of our "Prefer default Intellisense" option.