I used to shun EQ until I required my HD800. And now, the circumstances has me using it extensively, and I'm very glad that I am...
When I got my HD800, I knew immediately that these were pretty much tailor made for classical, jazz, and acoustic music and for these genres, I still prefer that they're left non-eq'ed to my ears. I also found out why many claim that these aren't really for mainstream genres like rock, pop, dance, rap, etc; the undeniable emphasis in the sibilance region in the HD800 prevented, at least in my case, from enjoying these overly much (and to a lesser degree, not enough weight in the bass). I do find that many songs in these genres are not mastered that well (specially in that sibilance region that typically seem boosted; though this is likely in part done on purpose to make an illusion of making it sound "clearer" on everyday speakers and stock headphone/buds that tend to be weak in this area), so with HD800 having an emphasis in this area it kind of compounds the problem, making it a painful listen.
This is when I started EQing my foobar to reduce the top end of the sibilance region (7-10k) my HD800's were emphasizing (not by much, maximum 3-4 dbs or so). This has increased my enjoyment of the aforementioned Rock/pop/J and K pop/dance/rap genres immensely, even with the HD800's that are supposedly not that great with them. Not only is the sibilance no longer a problem, but it also enabled me to boost the volume on my amp just a tad more, giving it the slight extra bass needed to enjoy those genres fully (before EQ'ing this is not possible to do, not before it kills my ears first from harsh sibilance anyway). It's only a slight decrease, and it is eq'ed down, so there's no problems with clipping/distortion that I can hear, and I can still turn it off if I wanted to enjoy the classical/acoustic genres fully. It just makes sense to do IMO to make the HD800's more of an all arounder.
So yeah, I now fully believe that EQ does have its place. You just have to fully know the qualities of the headphones/amp/source in question and then apply the EQ correctly.
Edited by K_19 - 7/7/10 at 8:20pm