I just installed Ubuntu 11.10 on my Windows 7 Box. It's a single boot. The intention was to install Ubuntu and destroy Windows 7 with a full erasure if you will. However, post install my PC was failing to boot due to Windows 7 being stuck in GRUB and not only being stuck but wanting to be the primary boot partition. There is no known trace left to Windows 7.
I installed Ubuntu a second time, hoping this would resolve the problems. It didn't, but I can boot into Ubuntu manually if I go through the boot selection at BIOS load, and force – in a sense – GRUB manager to load, so I can select from the list.
This is the third time this week I have installed Ubuntu onto 3 separate machines – all originally Windows 7 boxes – and this is the first time I have ran into this issue.
So I know it's possible, but there are more people looking to remove GRUB and go back to Windows rather than the other way around.