My wife has an early '09 24" iMac (3.06Ghz/GT130/4GB/1TB) that was operating perfectly with Snow Leopard. After installing Lion, it has become really unstable. It freezes often requiring a reboot, and occasionally it will kernel panic with a gray screen. I'm thinking it's possible that when the upgrade occurred, it didn't install everything correctly. I would like to reinstall Lion fresh on the machine. I really don't want to lose any data, as she has hundreds of GB worth of photos/music/documents. I'm tempted to wipe her time machine disk and do a completely fresh backup before I attempt a reinstall. What is the process for doing this? I'm afraid that if I use migration assistant and allow it to reload from time machine that it will restore whatever was causing the problem in the first place. The object is to have a completely fresh copy but keep all data. Any thoughts?