I bought the PX100 as a portable headphone after reading recommendations here and at headroom. They totally suck: Very strong, bloated, distorted bass, they lack detail and simply sound dirty. However, you can get used to crap and will not recognize it after intensive use. But when you switch to better phones (like HD-600 or Grado 325) you will recognize how crappy the PX100 sound.
Next worst buy was the Senn 595. Also bought them through overly exaggerated recommendations from head-fi and headroom. They are quite well balanced, sound neutral, but have a slightly dirty, grainy, plastic coloured distorted sound signature. The HD-600, Grado 325, Stax 3030 are much better !
I am still not sure, if my 2004 Gilmore Lite was a good investment. There seems to be a subtle improvement in the soun, sounding slightly cleaner, but maybe losing some detail in the midrange ?
Best buys: Grado 325, Senn 600. Stax 3030 are only slightly better (better detail, more liquid, but less bass punch) and cost much more.