The Pioneer DJM-5000 isn't just a mixer, its also a midi controller with a built in soundcard. So if you show up at a club with this mixer, you can plug your laptop directly to the mixer without an sort of interface (audio interface or controller.) There is also a unique zone feature which sends different audio streams to different zones. For example, you can use 2 channels to mix live to the main room and then hook up a CD or Mp3 player on a different channel to go to a different zone (or room.)
Perhaps the killer app for DJs is the microphone inputs which have a new advanced talk over effect where instead of lowering the music, it only lowers the mid's. This makes the voice talking sound better and doesn't affect the overall volume.
The Pioneer DJM-5000 is set for released in September with a MAP (Minimum Advertised Price) of $999 and MSRP (Minimum Suggested Retail Price) of $1275. If you are looking to upgrade the mixer at a nightclub, this should definitely be on your research list.