I have Lion DP 4 installed on a separate drive in a Mac Pro and Migration Assistant sort of worked but not really. Apps and most everything else had to be re registered from scratch. The reason I installed clean was that when I tried to run an upgrade install from Snow Leopard after repairing permissions, was that it failed and failed again etc. Shouldn't I be able to run the installer form within snow leopard, then at the end have all my itunes, calendars, address book and apps registered etc? Didn't work that way. maybe it will work on the final Lion version. Has anyone completed a successful in tact upgrade from snow lep to lion DP4 on a Mac Pro? I know there are issues with certain macbooks and some imacs.