I'll add this one: too formal for casual usage, too informal for any serious formal analysis. me? I prefer boxes and arrows on a piece of napkin if possible.

I agree, it is hard to beat a wireframe, functional specification document and a flow chart. UML tried to put the wrong part of the app into pretty pictures to make those who do not understand development feel comfortable. The problem is that it did nothing to help the actual project get done therefore it was rejected by developers who are generally under time constraints already.