Whats been said about speed brakes in this thread... what a load of BS.
The speed brakes are a normal part of the aircrafts flight controls - use them as appropriate.
Perfect example is when ATC tells you to keep the rate and slow down. You can be an ass and say that you are unable (hopefully they will sequence you behind the other more reasonable and professional pilots). Or you can help to make the traffic flow work by complying as best as possible within the limitations of the aircraft (witch includes the use of speed brakes).
Another good example of airmanship use of speed brakes is if you don't know how long your distance to go would be (for the Microsoft pilots that appear to have been commenting here, that would be in the case of where ATC is giving you radar vectors). For the sake of economy it would be advisable to keep a descend path somewhat between what you think would be the shortest distance and the longest that ATC would vector you). Thereby keeping the path just high enough that you can take the shorter distance with the speed brakes and the longer distance with a minimum use of thrust (=fuel).
Posters commenting in this thread, who are retired dinosaurs used to fly in an airspace as the only aircraft, are excused...