I had a bit of a hard time finding out (i.e. googling) how to list changed files in CVS using the command line.
The answer of course is easy:
cvs -n update foo
-n means "Don't change files". So you do the update, which lists the changed files (both on the repository and on your local copy) but the update isn't actually performed.
There you go. (The spellchecker didn't accept "foo"!)