I've updated my MacBook Pro from Maverick to Yosemite and has been running for about 2 weeks now. I had absolutely not a single problem with the update. At a point far into the update the update froze but I was able to restart my MacBook and restart the update no problems. It picked up where it left off and completed fine. The performance has been great. I also run VMWare on this MacBook for testing purposes. That updated and is running with no problems. Love the new features and look. I have had but 1 problem. I have a Western Digital DX4000 NAS that I've had installed for over a year. After the update to Yosemite my ability to connect to this NAS has been compromised. I talked to WD support. They confirmed the update as my problem and the kicker is: They have no upgrade plan in place to support running this NAS on this version of OS/X. Quite disconcerting. Apple's great. Can't speak to highly about WD.