I suggest that any time Parallels is resumed or restarted, it tests if any Parallels CDs (eg vmtools.iso) are mounted. If so, it pops up a messagebox, "Would turn off tools installation." Clicking yes unmounts the CD. I admit experienced users likely already know (or can figure out) how to unmount CDs, but new users ask about this every week, so I say make it easy for them.
