NYTimes has a little article about DJing with MP3:

Hard Disk DJ's 'Spinning' MP3s. NEW YORK (AP) -- Friday nights at Brooklyn's BQE bar appear like most others. By The Associated Press. [New York Times: Technology]

I have fairly mixed feelings on the whole mp3/digital mixing thing. On one hand I think it's pretty damn cool if it works. My friend Lukas has a DJ CD player that is actually fairly cool. But in the end for me there are things I just like about vinyl and using turntables.

The first is the tactile aspect. As I'm beatmatching I feel, as well as hear, how much I'm slowing down the turntable with my fingers. I feel much more connected to the record. Secondly, the visual aspect. By looking at a record, I can usually tell when there are going to be quiet parts just by looking at the grooves. I've found this invaluable when looking at when to start bringing in a new track.

Last but not least there's the issue that most of what I'm getting comes out on vinyl. Which would mean I'd have to transfer everything to digital as I got it. While not being that big a deal, it is a bit of a hassle. It would make it harder for me to pick up a new record and drop it that night someplace.

I don't think DJing by CD or mp3 is any less valid a form of DJing though.