Depending on the hotel, you can often get good recommendations. Some may be unscrupulous, and you may find the occasional lazy concierge who recommends the same restaurant no matter what details you give, but in general, decent hotels have to be able to recommend a fair number of good restaurants and, in my experience, the most common kind of bribe that a concierge will tend to get from a restaurant is a free meal, so if they like it (and they have decent taste), they'll generally steer you pretty well.

That said, if you are looking for a specific type of cuisine or a particular area, their knowledge may be limited and the cab driver/person on the street recommendation can be good. But it's key to make sure you frame it well--i.e. where would you go for a special occasion if you wanted to spend (no more than) XX amount of money? This way you reduce the parameters of their personal quirks/taste for a general idea.