Just want to throw in two quick things, both to faideelah (although joker, you may want to throw this in to your review). The K81DJ have been replaced by the K518LE. It's questionable whether the drivers have been changed; I for one don't believe they have been between the models (I don't think that AKG has developed a new driver in many years now, not that that's a bad thing). So, that means that the only two changes for the K518 are colored earcups, and more importantly, a shorter cord. I think that they're a little too short, but it will allow you to listen to your headphones with an ipod in your pocket. So, if you're looking to buy old-stock K81 then get the cord shortened to your liking by someone that knows their way around a soldering iron, but if you just want a short cord, get the K518. They periodically go down in price. Amazon had them as cheap as $50, less than 2 months ago.
As far as DJ headphones, in general they suggest thumping bass to be able to identify/control your tracks during a set, swiveling cups to be able to quickly hold the headphones up to your ear or pull one ear out to ambient sound, solid isolation (oftentimes through hard clamping), a long enough cord for a DJ to be able to move around the equipment, etc. With Ultrasone for example, the HFI-580 and DJ1 are identical except for the color and cord length. So, as was mentioned above, you have to take the "DJ" label with a grain of salt. The AKG don't have a DJ label anymore, even though besides the cord they're functionally the same. As a word of warning, they're pretty uncomfortable for long periods, but oh man is the sound worth it. I actually have them plugged in right now.