Hi, I have posted here a few times in various posts with regards to my issues im having with my rMBP and Mountain Lion. As I have noticed from a number of you you are also experiencing the same issues as me. Graphics glitching in safari, system wide UI lag and terrible system wide audio stuttering. Well I have just got off the phone to a senior Tech guy at Apple. He has got me to run a multitude of system report and tests that he will be sending to the development team. Whilst I was waiting for them to complete he spoke to them and checked their internal bug list. His response was there was NO KNOWN issues within Mountain Lion or with the rMBP having any of the problems I have listed. He followed to say he has never experienced these himself either. I have to wait 3-4 days for him to get back to me, after the development team have analysed my system logs. However the first tech guy I spoke too, when I explained the problem said "oh these retina MBP seems to be having lots of problems" :/ So in short, those of you hoping that 10.8.3 would fix or address these issues (as I have been hoping) are going to be very let down with this update I believe. Thought I would share with you here.