I have it on good authority that the way the OS gets installed on the assembly line has subtle differences to the way the installer disc does its thing. I have also heard that most of Apple's internal testing is done using machines that have been wiped and then "fresh installed" using the bundled disc. Because of this, I always wipe a new Mac when I get it and do a clean install from disc. Some people may think this a silly and unnecessary step, but I have been running my 2010 i7 MBP that way since it came out, with only one or two crashes in almost a year of hard use, and they were almost certainly my fault, not the machine's. If the folks at Apple suggest a clean install, I would definitely try it, even if the above rumors no longer have any basis in reality.