I had a platinum when I was working for Booz|Allen|Hamilton. Was very handy and like others have mentioned. Having access to a concierge, club rooms, etc was very handy and appreciated when traveling 40% of the time. Well worth the extra money.
Now though, they offer the Platinum card to everyone, just like they do the Gold Card. It's no longer a sign of good credit or anything else. They just want your $$$ and the Platinum card is running about $350 a year plus $150 I think it is for an additional card.
Now apparently if you want to impress folks you need a black card so you can post it up and attempt to impress some folks on the web... The Platinum and Gold cards just don't do it.