I have a late 2013 MBPr. I have been using 10.9.3 and I love it. It is smooth, snappy and just works. The only issue I was having is an occasional delay in wake from sleep but I am OK with that. My question is, can I just plan on using 10.9.3 for the life of the computer? I really don't want Yosemite at this point or even 10.9.4. I am afraid new issues might arise. While my computer is running great, I just want to leave it that way!