This is covered explicitly in the OSDev Wiki.
Basically, you either have to implement runtime support for certain things (like RTTI, exceptions), or refrain from using them (leaving only a subset of C++ to be used).
Other than that, C++ is the more complex language, so you need to have a bit more competent developers that won't screw it up. Linus Torvalds hating C++ being purely coincidental, of course.
