Are people really in the habit of moving every single time they don't need a variable anymore? Unless you're in the habit of doing that, option 4 is totally opaque and you wouldn't know to take advantage of it without reading the implementation. I think that's kind of in line with what Kylotan was saying.
For me, using move semantics in the context of this is somewhat equivalent to using reserve on a collection class like vector. I just get some efficiency for a little bit of additional thinking/design overhead. So yes, whenever possible (in places where it can matter) I tend to move expensive temporaries (like string, vector, ...). However this mostly means that I adjusted my design. IE, where you would usually see something like this:
Foo foo;std::string& string = foo.GetString();string = "Test";string.append("whatever");
Or something along those lines, I would instead do:
std::string string = "Test";string.append("whatever");Foo foo(std::move(string));
I find the latter much cleaner, especially in non-fabriacted examples
Obviously you could have done this before without the move-semantics, but it would have most likely invoked a copy operation for the content of the string.
EDIT: i think i misread your question. Anybody who is actively using C++11 surely has at least a basic understanding of how and when to use move-semantics. Anyone else wouldn't have that knowledge, so its probably a matter of who you target.