Developer: The Access Network Media and Technology Company, Inc.
Price: free Download on the App Store
There are several good restaurant review apps in the AppStore (my personal favorite is UrbanSpoon), but they all suffer from clutter - the hip, trendy sushi spot that you really want to go to is listed right next to the neighborhood Jack in the Box. BlackBook solves this problem by focusing only on those restaurants (as well as clubs and hotels) blessed by the cooler-than-thou editorial board of BlackBook Mag.
The design philosophy of the Blackbook App is "less is more". There is no way to search for cities, or even type of cuisine. BlackBook justs locates you via GPS and gives you a list of the top 20 places near you that you should consider. This solves the problem of "where's a good restaurant/hotel/club" nearby, but its not very good for planning your next vacation or even a dinner accross town. But, you could argue -- that's what the website is for (and the actual website does allow you to drill down by neighborhood and cuisine).
In random tests near Santa Monica, the BlackBook guide was pretty much spot-on. It consistently surfaced the spots I would consider to be the best in town. This is an app you will want to bring with you on your next business trip...