Update: If you're having a similar problem, try leaving it on on the grey boot screen overnight (ie several hours). In my case that seemed to resolve the issue. What the issue was remains a mystery. As I , and others have discovered, the latest ML update completely messes up your hard drive layout to the point that Bootcamp/Windows will not start. To give you an idea how much it screws things up here is my disk layout *after* the update: gpt show: disk0: mediasize=751277983744; sectorsize=512; blocks=1467339812 gpt show: disk0: Suspicious MBR at sector 0 gpt show: disk0: Pri GPT at sector 1 gpt show: disk0: Sec GPT at sector 1467339811 start size index contents 0 1 MBR 1 1 Pri GPT header 2 32 Pri GPT table 34 6 40 409600 1 GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B 409640 291015616 2 GPT part - 48465300-0000-11AA-AA11-00306543ECAC 291425256 1269536 3 GPT part - 426F6F74-0000-11AA-AA11-00306543ECAC 292694792 1272 292696064 1174642688 4 GPT part - EBD0A0A2-B9E5-4433-87C0-68B6B72699C7 1467338752 1027 1467339779 32 Sec GPT table 1467339811 1 Sec GPT header </sigh> Short of completely wiping the disks and starting from scratch (but how without ML disks?!?) I have no idea how I am going to fix Apple's monumental **** up. Don't they test their damn patches? This one was specifically for the rMBP so it's not as if they have a lot of variations test?