I remember once seeing an impressive example of what hdr is capable of. The example hdr image was a lit light bulb. (The image in that example was created from a set of photos each taken with a different exposure. My understanding is that the technology has developed with some cameras now capable of creating the hdr image in one shot). Because of the wide dynamic range in the light bulb image it was possible to adjust the image in software until the logo printed on the end of the bulb could be seen!
Wikipedia is a good place to learn about the technology: "The wider dynamic range allows HDR images to more accurately represent the wide range of intensity levels found in real scenes, ranging from direct sunlight to faint starlight".
Regards, Ross