So...updating an application that uses MSDE as a database - it happens
to share a MSDE instance with some other applications. The update
uninstalls the previous version before installing the new version -
fairly standard stuff.
Ok, why is the update process complaining about x app running on the
MSDE instance? Uh oh, the 'I've got a bad feeling about this...'
doesn't so much settle quietly, rather it gives me a swift kick in the

Yup, the update *removed* the MSDE instance as part of its update - no
warning, it just pulled the rug out from under the other applications.