There are 3 different call centre concierge in Australia, depending on which credit card you have. I worked at 2 of them, before starting my own personal concierge company.
I wrote a blog post about this very thing, after I had worked at the first call centre, but before the 2nd one - I can't post links so please search for 'putting the personal into concierge' on the Concierge Connections website.
To be fair, the second one (Visa Concierge) is much better, as they do take your credit card details, store them securely of course, and so can make purchases (eg - tickets on your behalf).
Also, the call centre concierge I am referring to in my blog post was over 2 years ago. Their procedures may have changed, and I am sure their staff has.
I still stand by my comment that you get what you pay for in life, but credit card concierge is worth a go (you don't know til you try it, right), and as others have pointed out, the result largely depends on which concierge you get.
Also, to clarify a few points which have been made...
* Usually you won't pay more for something through a concierge, than if you found it yourself. If they do quote you more, they are not trying to rip you off. They might not know a great website/deal that you do. If you have already found the flight/product etc cheap somewhere, tell the concierge that you are wondering if they can beat that price.
* Some things will be quicker for you to do, than to explain it to a concierge and wait for the results. Other requests such as accommodation in 6 cities in Europe will probably take you hours.
* They have access to translation services and often members of the team will speak various languages, so they are definitely worth trying for requests where you need to call overseas and their English isn't great.
* They do have access to sold out tickets, although the ticket provider will charge a premium fee for these.
* They do not have an allocation of tickets.
* They will also queue on the phone/internet for you, when a popular event goes on sale. This is priceless if you have a meeting scheduled at the same time, or can't be bothered queuing. They cannot guarantee they will get you tickets this way, but the odds are higher than you trying by yourself.
* Yes, Amex Concierge has reserved tables at top restaurants. They often book out in advance, but not as far in advance as the non-Amex tables.
NB - all of my comments are based on my experience of working at the 2 call centres. Things may have changed since I was there.
And yes, my company can do all this plus more. Check out Concierge Connections.