Pros: Comfortable, smooth
Cons: None, really...they're not wireless...
These headphones make you forget you are listening to headphones. They are so comfortable, so natural sounding, they are a joy. They have enough oomph to rock out (I don't think they are the ultimate electro/synth/rap cans) and yet present the most delicate classical music.
After about 12 years of CONSTANT use they finally gave up the ghost. Sent them back to Sennheiser for repair and was told they were beyond worn out. Got 50% off for a new pair of HD600s.
I cannot think of any piece of audio or video equipment that gave me more pleasure for the money than my HD580s. Best bang for the buck I ever had.

Can you compare the 580 to the 600 soundwise and comfortwise?
First impressions are that the new cans are very detailed and accurate, but dry and technical sounding. I find myself wanting a tube amp to warm things up a little bit. At this point I would say I preferred the sound of my 580s, however must emphasize that these are FIRST impressions, and I'm holding off final judgement for at least 50-100 hours of listening. Again, detailed and technical, but the sound hasn't really pulled me in yet. Will wait and see, meanwhile, I'll be looking at tube amps...