There are a few notable differences in our impressions, but none are drastic. First, Tyll mentions that imaging isn't as strong on these as on others. While I do agree with that compared to the very best, I find them no slouch in this department. I find they do a great job on imaging, especially in the frontal region, particularly the center image, which is my #1 priority. The PM-1 is, so far, the only planar (magnetic or electrostatic) that has an acceptable center image, and it does a good enough job just off-center as well. Previously only the HD800 was able to do this for me, and while the HD800 still does it better, the PM-1 is in rare company.
I'm in agreement on the imaging, I find these cans to be on par with anything else I own save the HD800s.
I was going back and forth between the PM1s and the LCD-X (only other planar I had) for a long time. While i felt the LCD-X had slightly more dynamic range the PM1s just sounded better a lot of the time, especially if the music was focused in the midrange. I think it just handles that area exceptionally and that just overwhelms any deficiencies.