This question already has an answer here:
I upgraded from Snow Lion to Mavericks and just found out that I can't sync my address book and calendar between my iMac and iPhone (3GS) using iTunes. I'm not using iCloud and not willing to use it either. All my data files (from Mail etc.) are also "upgraded" to Mavericks. Is it possible to reinstall Snow Lion and use Time Machine to place all date files back or am I going to be in trouble here?
Added: I meant Mountain Lion (in stead of Snow Lion -- sorry ;-))