Having left the update to settle until November, I was stupid enough to download and try to install on my late 2013 Macbook Pro Retina 13, 16Gb ram etc.. I was tempted through the promised improvement in wifi, which has been pretty dreadful in Yosemite. It stopped at 90% bar for some hours, tried all manner of reboots to no avail, just went back to the apple logo and the 90% filled bar. Next day the same. After hanging on support for 40 mins, they tried and failed to remedy, as I had, with reboot safe, reset PRAM, etc etc. It would never properly reboot. Disadvantage of a fixed battery. No way of getting it to reboot properly. Even Alt key for network boot failed to work. Tried to get a Genius appointment at the nearest Apple Store, to discover an 8 day waiting list. Now getting annoyed, as the Apple software update broke my working, less-than-two-year old MBP. Not me. Called to no avai, drove all teh way there to be given a 'turn up tomorrow first thing and we'll try an get you in. Did that, 30 mins after opening time, to be told sorry, nothing until 1.30pm. Hang around and we'll send you a text. Running a company, time is money and this was getting beyond a joke. Anyway, took a patience pill and eventually met the tech at 1.50pm. TWO hours later at the now less-than-appropriately named Genius Bar, the result is a wiped drive and start again with new install of Yosemite. Fair do's, he did try. Maybe there is a little nugget of genius there... no El at all... Now spending another half day re-loading all the programmes. So heed the warning. Don't be tempted.