I just tried to reinstall Lion on my MBP. I rebooted the system and held down the Option key to go into Recovery mode. Then I told it to reinstall Lion onto the Macintosh HD drive. So it spent the next 2.5 hours downloading Lion. Then it rebooted and started installing Lion, and that took 30 minutes. Then it rebooted again, and I was shocked to see the lock screen for the old user I had. I logged in, and it was as if nothing happened. All my browser windows were still open along with the other programs I had open before reinstalling. I thought a reinstall was supposed to make a totally clean system. What the heck happened?