If you do a seach on the FT Amex board, you will find plenty of comment about the shortcomings of Quintessentially.

However, fundamentally people ask too much of them (or they promise too much). Let's imagine I run a very popular restaurant which is full every night, although I always keep back a couple of tables for my friends or regulars who pop in at short notice. I am turning away 50 table requests a day from the public. Why on earth should I open up a table to a Q member? The only reason I would do it is if I thought the Q member would spend more than a general member of the public, which is possible although not certain unless they were on the top level of Q membership. And apart from restaurant bookings, all they are doing is sourcing stuff for you online which you could do yourself.

There was a very telling piece in the London Evening Standard a year ago. A reporter rang 10 top restuarants asking for a Friday night table at short notice. All refused. The reporter then called back saying she was the PA of a banker who had just got a £1 million bonus and wanted to treat his wife to a special night out. 9 of the 10 restaurants mysteriously found that they did suddenly have a table available.