Wild that this thread has been cooking for fifteen years and the issues remain the same. Kinda comforting in a way. I just wanted to chime in on two points - first is that the SM57 and 58 are reliable, workhorse live performance mics. We would joke that if I misplaced my hammer, I could always grab a 58. They're fantastic mics - not the clearest, not the "finest" - but as workhorse reliable sound reinforcement they have no equal in my book.
Second is to echo Rob's warning that their popularity made them an obvious target for knockoffs, and the easiest way to get ripped off is to buy them on ebay. For these mics, stick with a local reputable dealer. The local dealer can match the catalog pricing anyway and you can be certain you're getting the real thing. It is hard to tell by looking because the knockoffs look identical, but they sound like hell. Buy these locally and you'll be fine.