So far I have had a couple of good experiences with the concierge. The first one was getting tickets for Cirque du Soleil O in Las Vegas, calling in the morning for the show that same evening. The second one was just last month, when they got me a reservation at Le Bernadin, in New York, with about ten days notice. And later they were able to add an extra person to the party, completely last minute.
Since I'm quite of a football fan I regularly call them about tickets, but find them consistently expensive, due to always resorting to their 'alternative' providers. No luck so far in that area with them.