Putting it on my 2011 MBP, see signature. Hours later after the start of the upgrade (downloaded it last night), shows only half installed and progress seems glacial. Now I realize this could be a function of relatively limited Hard drive space, due to the OS download at the start of the upgrade process. Would you agree? I've got other computers in the house, and I'll let this chug away for the rest of the day if I have to. But I thought I'd ask, is there reason for concern? I'm looking at a grey screen with an Apple in the middle and a progress bar. Fortunately I have a Mavericks Time Machine backup.