Just a warning: On Oracle 10g this made my database completely unusable. I couldn't even login using SYSDBA. I could stop it but not start it again.
It didn't matter too much because it was a development database that I wanted to drop the data from, but it did put the database in such a state that I couldn't reload a new file into it using imp.
Instead I've had to use the Database Configuration Assistant to create a new blank database again.