Djing with a laptop(or computer) is something that is fishy and has a very very large amount of flexibillity and also levels of complexity.
Depending on levels of complexity mixing with a lap top is either completely pathetic or absolutly wonderful.
If you use a lap top and have two tracks with eq's and a sound card with two output channels and prewarp all your tracks and simply trigger them, and use the eq and crossfader to mix then it's pretty damn pathetic. Anyone can do this and anyone can become a dj. It takes ALL skill out of djing(I don't care if you say beat matchign is half of it... that's true but it makes the whole process about 90% faster and easier)....
On the other hand, if you got your stuff together and you understand ableton and have a complex set then it is wonderful. If you remix tracks live, strip drums and replace them, mix four tracks at the same time... sample, resample, stretch and rearrange stuff on the fly it makes a wonderful show. It becomes a live performance instead of a traditional dj with two decks.
Also you could take ableton as far as running two separate copies of it simotanously on one machine running to two separate outputs to a real mixer, and you can use something like the m-audio dj interface and you can make them act like real decks.... to a point where you don't even need the screen and all of a sudden you find yourself breaking free from software and being completely hardware and it becomes a real dj experience. All this would require is some advanced midi knowledge to modify the message the wheels send.
Anyways, like I said, I have zero respect for people who jump on a set with a lap top and an m-audio xsession(pro) and does what I mention in the very beginning to get easy fame and easy recognition without having any skill at all when it comes to production or real djing.
On the other hand, if you use it to really manipulate sound(which is what live is for anyways) then big props to you.
I'll stick to full live performance of my tracks though thank you very much
[edit]Oh one thing I fogot to mention.... LOSE THE DAMN MONITOR/SCREEN... you can't perform and hide behind it, it looks VERY bad!!!!![/edit]