So C++11 has these cool move semantics... but when would you not implement move construction and move assignment for your type?

When to make a type non-movable in C++11?

I was surprised this didn't show up in my search results, I thought someone would've asked this before, given the usefulness of move semantics in C++11:

When do I have to (or is it a good idea for me to) make a class non-movable in C++11?

(Reasons other than compatibility issues with existing code, that is.)