Pros: Maybe the best phone for classical, lean, clear sound
Cons: Not ideal for rock
Although I also own a HD800, I'm keeping my AKG K701 for its combination of comfort and performance with classical music - in which it excels. Aside from the Beyer DT-880, the most comfortable headphone currently made, the K701 has plush velour pads (though users with bigger heads may prefer a larger phone). And the illusion of head space is equal to that of the DT880 and Senn HD800, making this phone easy to wear for extended periods of time.
The bass (or rather, the relative absence) is the sticking point for many. I believe that the sound is nicely balanced, but there's no question that it struggles to manage music with a more assertive bass presence. The phones have a ribbed top, and automatically adjusts to one's head size; however, many users will need to change their orientation so the phones fit perfectly all the time. Not a problem for me, but others have even tried to fix matter themselves.
However, I believe that this has been my best stereo investment. And if you look at the sell lists, you'll always find discounted phones for as little as $210 - a steal, in my opinion - and sometimes even less.