I had to use Ghost to come back to a previous version of my computer after installing version 4. I installed it over version 3.1 and it was a mess. Check the many sites discussing this major problem with version 4.
Today it took 4 hours to try to install it. It worked but installation was not perfect. I had to mess with the Registry Editor and delete anything related to Apple manually. In the end, I could not see the Control Panel; but it worked. Using the Cloud to manage my contacts messed my Outlook contacts. It merged them with Linked-In contacts. I will stay with 3.1 which works fine with me. The only thing you get with version 4 is the iCloud space to share files. I have no use for that.