I've had my HD800's for three months now and I am only now beginning to get them "managed" to the point that I am really enjoying them. My initial impressions of these phones were pretty negative I suppose, but I am seeing the light now.
In my case so far I have changed out my interconnects to a set that seem to favor midrange more and adjusted the gain settings on my amp. And after the first few days I decided to just hook them up to an old CD player and run them continuously on loop for two weeks. I understand what everyone say about break in, but it did seem to smooth the sound out somewhat.
Bass is there with some good slam on the tracks that have it. It's a disciplined bass though, with no bloom or exaggeration. A couple of old tracks I use to test these phones and bass are David Bowie's Bring me the disco king and PJ Harvey's Working for the man.
These are great phones, and once you have heard them there is no going back to whatever you had before. I can only last a little while nowadays with my HE-500 or HD650 before missing the 800s.