I upgraded from 3 to 4.0 and had problems burning, so I dragged 4 out of the applications to the H/D and reinstalled 3. Everything went fine but I still wanted to se the Music Store and liked the idea of AAC encoding. When 4.01 came out I heard that some issues were addressed so thought I would give it a try. I upgraded and 3 became 4.01 in the Application folder. It seems to be working fine now. My question is; can I trash the old 4 from the HD (says cannot delete because belongs to system), but I should be able to run Tra**** or Super Delete, or will my playlists disappear along with the program?