Yeah. My problem with the em-dash is that it has too many uses (parenthetical statements, independent clause, verbal pauses) and as a reader you don't always know which one is intended until after you've read a bit past the em-dash, and might need to go back and reread the sentence once you figure out how it is supposed to be parsed. Use of semicolon and parenthesis are much clearer in contrast. The comma has the same problem to some extent. I would be happy if we could settle on consistently replacing some specific uses of comma with em-dash to make writing less ambiguous, but in the real world I find it clearer to just avoid the em-dash all around.