I've just made a bootable USB version of OS X Lion and went to do a clean install to leave my iMac like a brand new machine with nothing else on it. I powered off my iMac and plugged in my USB Pen Drive and started the iMac while holding down the ALT key which brought me up the menu where I booted from my Pen Drive. I selected Clean Install from the menu that appeared and after quite some time OS X Lion installed but with all my User Accounts and Data still there ? What have I done wrong? Would it be ok just to create a new User Account and delete the old ones or is it best to reinstall again?