I have had my my mbpr 4/128 since a week ago Tuesday. The first 2 days it hung. I have used a USB3 hard drive for time machine in the morning and then eject for the rest of the day. I have had no further hangs since then. My sys log though shows a constant flow of track pad errors.
I use this as background for what my evaluation is of this machine before I send it back for reimbursement.
I worked as a mechanical engineer for over 30 yrs and have used mostly UNIX and windows to run heavy duty
modeling and design programs. Of coarse never a problem with UNIX and all ways a problem with windows.
Unfortunately Mac machines were not supported by these design programs probably because not enough companies used Mac OS to make it cost effective for development although AutoCAD did try at one point and gave up.
My wife gave me a Ipad2 for Christmas 3 years ago and I was shocked she spent that kind of money for a toy.
That Ipad has been the most used and trustworthy device I have ever owned including my wife. So my old Hp
Pentium XP is on and has been on its last leg for a year and I told her I was so satisfied with the Ipad I going to wait for the new Mbp to come out and I going to get one even though it wasn't in the budget. And that leads me back to the beginning. I love this Machine. I was surprised at how easy the OS is to use and how blazing fast it is.
I will buy another one when the problems are fixed but I am going to get the 8/256 just to future proof incase I find some ram eating programs. I sorry to be so long winded but being retired I have that right. I turning this off and packing it up and will follow this thread until it is resolved