There is a bug in StuffIt Deluxe 7.0.1 if you run it for the first time as a non-admin user.
I have been sitting on SD 7 for awhile and finally installed it yesterday and immediately upgraded to 7.0.1 under Mac OS X 10.2.
My user account is _not_ an admin account so every time I ran StuffIt Deluxe it asked me if I wanted to register. It didn't matter what I answered or whether I checked the don't ask again checkbox. This was getting frustrating so I ran fs_usage on the pid of StuffIt Deluxe and it was trying to create a preference file in /Library/Preferences/. As a non-admin user I don't have permissions to do this so it was failing.
I fixed the problem by changing the permissions on /Library/Preferences/ to 0777 and running Deluxe again. Now the problem has gone away.
StuffIt Deluxe should be storing it's preferences in ~/Library/Preferences.