Another newsgroup nugget from Allen Bauer on b.p.d.n-t:
One thing you can do with all versions of Delphi from at least D5, is use the "-r" command-line switch. This allows you to specify the root registry key to use when loading the IDE. For instance in D7, you could export the HKCU\Software\Borland\Delphi key to a file. Then rename the "Delphi" key to something else, like "SafeMode". Then re-import the exported key to recreate the HKCU\..\Delphi key. Finally, when you run the Delphi32 application, just pass the "-rSafeMode" switch to use that key.
I think this feature can be very useful.
According to another post in that thread, there seem to be more undocumented switches: -s, -k, -q, -x, -y.
I have no idea what those are for...