I have a Mac laptop, set up to dual-boot OS X and Ubuntu, using rEFIt.
I just tried to upgrade my Mac laptop to the latest OS X version. The OS X installer would not do the upgrade. It printed an error message: "You cannot install Mac OS X on this volume" It also said "Mac OS X cannot start up from this volume"
The fix is incredibly simple: just uninstall rEFIt. Then the OS X installer is happy again.
I didn't know to do this, so I backed up my entire hard disk, wiped it, and then performed the install to OS X. (I'm not bitter... I made a few improvements to the disk partition layout while doing this.)
But I urge you to put an item in the FAQ, with the error messages, and the simple explanation that uninstalling rEFIt will sort the problem out. Then Google searches on the error message text will land users on the rEFIt FAQ and they can find this out.
FYI, here is a web page from Apple discussing this error. (Sadly, they do not mention rEFIt as a possible cause of this issue.)