If you have a mid-2013 MacBook Air, Apple released a recommended EFI firmware update this afternoon, version 2.7 which addresses some Boot Camp issues:
MacBook Air EFI Firmware Update 2.7
This update is recommended for MacBook Air (mid 2013) models.
This update addresses an issue which may cause a black screen to appear when installing Windows 7 or Windows 8 using Boot Camp Assistant if both an external optical drive and USB thumb drive are connected to the system. This update also ensures that the system will boot by default into OS X after installation of Windows 8.
The update file size is 4.8 MB and can be found on your Mac by going to the Mac App Store then clicking on the Updates tab.