Beautiful pages. I would just add one thing. People usually like to know the sensitivity of their headphones. In case of IEMs, a very high sensitivity (usually >112 dB/SPL) means the IEM will hiss with certain sources (like iPods), but that they will also sound louder when the player is set to low volume, thus saving battery juice.Shure E500, UE Triple Fi 10 Pro and Westone UM2.
Very wow sensitivity IEMs (100dB/mW or less) won't have hiss problems with any sources, but some people will hook them to an amp to make them sound better. Etymotic ER4S is an example.
Personally, I prefer when sensitivity is set in the middle, so that the IEM takes the best out of the two worlds.