I had good experience with clean installs of lion developer previews on my 2009 iMac. When the GM came out, I upgraded my current Snow leopard partition. Needless to say, the performance is awful. I used Onyx and the Lion beta of Cocktail to run maintenance scripts, repair the startup disk and its permissions, clear the user and system caches and logs, repair launch services and prebindings and rebuild spotlight. I have iStat menus installed so I'm always monitoring cpu and ram usage. With 70% of ram usage and 10% of cpu usage, I can't watch a low resolution avi file and browse with safari at the same time. Finder is a nightmare and everything else is sluggish at best. I'm out of ideas. anybody has one?