There is some truth to the notion that concierge service is overrated, particularly in a city like London, where there are a lot of very good hotels with a demanding clientele. On the other hand, I have found that in some cities, good concierges can really enhance the experience - one example (apart from the One Aldwych recommendation) is the Park Hyatt Tokyo, where the service and the perceived "clout" of the hotel do seem to help you get to where you want to go.