Pros: Huge soundstage, high speed, great with all types of music. Very comfortable.
Cons: Very picky about source and amp. Cable is arguably poor, so overall expensive to get the best results from. The painted plastic frame is a bit tacky.
I'm going to borrow a quote from jpelg who sumed them up nicer than I can in one of the meet threads:
After finally hearing the HD800's (both balanced & SE), I can understand the varied impressions that resulted from these this past year. They are quite the chameleon, sharing qualities with the venerable HD650, as well as electrostats. Again, the reference quality is clearly evident, and they are very sensitive to changes in associated gear. I'd even go as far to say that they are a bit finicky, because one errant piece of gear, or even recording, can cause them to lack a certain cohesiveness. Still, they are top cans, and worthy of spending time & money building your system around.