I have a 2007 iMac with 2.16 Ghz and 4GB of ram and I installed Lion today and I very much regret it. The computer constantly freezes or restarts and when I try to repair disk permissions to see if that would help it freezes immediately as I hit the button. Is anyone having a similar problem? or have any ideas on what to do to fix it? I have not spent even half an hour on Lion without it freezing or the screen turning black and restarting. This is incredibly frustrating. It seems I have to revert back to Snow Leopard if anything.