Remember Dudley "ain't no law against bein' a asshole" Hiibel (previous entry here)?

He lost.

UCLA law professor Eugene Volokh examines the decision here (also here and here). As I understand it, you don't have to provide ID on demand but you do have to give your (real) name. Also, since the decision is that the demand for your name does not violate the US constitution, what it really means is that state laws requiring you to give your name are not unconstitutional. Some states may not have such laws (yet).