Wired.com has a review of the Tonium Pacemaker Portable DJ Machine, and decides it’s cool, but an expensive toy:
The Tonium Pacemaker may be modeled after the idiot-proof iPod, but taking advantage of all the features on the Pacemaker requires an inordinate amount of button pushing. Fiddling around with it while sober requires a certain amount [...]

A live performance with the Tonium Pacemaker - the pocket-sized DJ system, performed on Beatport’s stage at Hotel National, Miami, March 29th 2008.
I’m still not sold on the idea of a palm-sized DJ system. How can you work this with any level of control.
Anybody want to set me straight?

Tonium Laboratories has released Pacemaker, the world’s first professional pocket-sized DJ system.
Yep - now you can put a dj system in your pants.
Pacemaker allows two tracks to be played simultaneously and boasts all the functionality of a full, professional DJ set up. The intelligent software will automatically work out the BPMs (beats per minute) of [...]