Here's the Scoop:
Decorated dinnerware falls into two categories - underglaze and overglaze.
With underglaze dinnerware, the decoration is under a layer of glaze, so it's protected. With overglaze, just the opposite is true; the decoration is unprotected.
Some metal-trimmed dinnerware is underglaze, which means the dishwasher can't hurt the trim. The trade-off is that using this technique makes the metal trim look much less shiny, so a lot of metal decoration is overglaze.
You really have to assume that dinnerware with metal trim is overglaze unless the dinnerware is marked underglaze and says "Dishwasher Safe." Don't assume that just because something is marked underglaze that the metal trim is underglaze, too - it could be that just the rest of the pattern is underglaze. It pretty much has to say "Dishwasher Safe" before I'd trust it in the machine.