If it has a spike around 10kHz it is like turning the contrast up on your TV, or sharpening a picture in photoshop. The Etymotic ER-4S, ATH-CK10, Sony MDR-7520, Sony SA-5000 all have a natural spike at around 10kHz.
Not everyone has the same equal loudness contour, so some people may hear the spike louder than others. I'm not sure what the dB deviations are from person to person.
Edit: goldenears.net notes a spike around 7kHz results in more fineness too, in efficient headphones (see the Dynamics part), but I personally find that one a little more offensive.
Edited by kiteki - 7/2/12 at 1:15pm