1. Plat concierge got me tickets to Leno in Las Vegas, the seats were moderately better than I could get myself online or on the phone, for the same price.
2. Plat concierge got me tickets to Cirque du Soleil "Mystere" in Las Vegas, the seats were much better than I could purchase directly, for the same price.
3. I used them to try and make restaurant reservations and they were not too helpful, they e-mailed me a list of restaurant suggestions that was cut-and-pasted from Frommers.com, I didn't end up reserving any restaurants through them.
I haven't used the platinum concierge for anything else as I have had my platinum card for not too many months.