Sorry if this is a new iteration on a tired old thread but.. I have a 5.5yr old MacBookPro 19inch. Bought the max of the max at the time to future proof it.. and that served me very very well right up until the free launch of Mavericks. I'd never upgraded my OS once but since Mavericks was free I thought, why not? BAD MOVE. It KILLED my machine. Since then it has been operating like a windows machine - unable to perform super basic tasks without freezing, takes literally 3-5 minutes to open applications - sometimes longer, cannot run more than 2 apps at once without freezing, everything is dead basically. So I was desperate for the new iMac but thought maybe I should wait till it ships with Yosemite pre-installed? I can handle not having the latest 4k display and Broadwell chips (if they are indeed coming soon) but I don't want a repeat of the Mavericks fiasco where my perfectly OK machine suddenly dies with a new OS. I guess the obvious answer is buy a new Mac and don't upgrade the OS when Yosemite comes out - but there are some functions in it that will be very important to how I work, not least being able to make phone calls from the computer. I'm also at the end of my contract cycle with the iPhone so likely to be getting the iP6. Just wondered if anyone had thoughts. Was I just unlucky with Mavericks? Can one normally upgrade the OS and NOT affect the machine overly?