Grado's and Hifiman's are complete opposites when it comes to weight, except for the Grado's with metal ear cup designs. I remember the PS1000 being quite heavy as well. If the idea of wearing a heavier phone than your current Grado SR80i would put you off then I would steer you in the direction of Sennheiser or Beyer Dynamic. If you are fan of the Grado sound, then something like the Grado RS1i would also be a nice choice. Those wooden earcups are quite lightweight.
I had the Grado RS1i as my main headphones for about a year and they are probably more than twice as light as the HE-500s. When I got the HE-500 my neck muscles were quite sore for the first two weeks or so and then I became used to it. The headphone padding and ample space in the ear cups made my ears feel more at home compared to the Grado's on ear design. That said I have had lots of people trying my HE-500 headphones who were immediately put off by their weight, so it is definitely a very important consideration when picking these.
Edited by daerron - 9/13/13 at 12:45pm