Gee – thanks Mastiles! Well, the point is that you can overcook the effect all too easily. But then again, they are good for creating a certain effect – dont think of them as photos because they are heavily manipulated.
The technique is supposed to enable you to capture more of the range of brightness in a scene. Often it is difficult to expose a photo correctly to capture very bright and very dark areas. This method merges 3 or more images exposed for different parts of a scene. Thus you can get more information and capture more detail. Its particularly useful for pulling the detail in the sky out. The consequence of this though is that the algorithm can make things look unrealistic or cool or crap or arty. Depends on your point of view.
In my case, I tend to go quite light on the HDR effect and then manipulate things in photoshop afterwards with the aim of creating a particular effect – e.g. eerie looking castle.