I’m giving the OS X Yosemite beta (10.10) release a try on my RMBP mid 2012 model. A number of people had reported a few issues with download speed but I had no trouble with it last night. From end to end I would guess it took a little over 20 minutes to download and install. The most obvious difference is the flat looking UI which is fine with me. I have had no trouble with anything on the MBP so far but got a notice that iTunes 18.104.22.168 was available so I am giving it a try as well. It looks a little different but no issues either at this point. Check back for more to come.