If you install Windows 7 into the Boot Camp partition from a USB drive, it will apparently become impossible to boot from that USB drive on that Mac again. I'm trying to find out why.
This is the sequence of events (normal & boring):
Create bootable Windows 7 Setup USB drive (the usual way: diskpart, clean, create partition primary, etc, etc)
Prepare Mac with Boot Camp Assistant and rEFIt.
Boot Mac from USB drive (works great), install Windows
Everything's great, Windows works, OSX works, rEFIt allows booting either one
Now the strange part:
Insert the bootable USB drive again (because, I don't know, I want to run the repair tools on it?)
Reboot Mac and choose USB drive from rEFIt menu
USB drive is ignored and the machine boots straight into Windows
In fact, the only way to boot Windows Setup again on this computer is from an external DVD drive, with a Windows 7 DVD in it. Selecting the DVD in rEFIt boots the DVD. Selecting the USB drive (if both are plugged in) also boots the DVD.
Removing the Boot Camp partition from the Mac makes the USB drive bootable again. It seems that whatever bootloader code is executing either from the EFI or from the USB stick tends to prefer any bootable DVD or Windows HD partition over the USB drive. If none are present (DVD unplugged, Windows partition removed) the USB stick boots.
I realize it's an esoteric problem and the DVD workaround is kind of acceptable (even though a PITA), but I'm curious if anyone has an explanation.
(Please don't migrate this to the Apple site. This is not an Apple-only question.)