Tools available to DJ's have changed dramtically over the past few years. First CDJ's were introduced, allowing DJ's to not only mix two CD's together but also allow a fair amount of digital trickery such as looping or changing the speed of a track without changing the pitch. Traditional vinyl DJ's at first derided this new way of mixing, but it slowly gained acceptance. These days you'll see DJ's mixing it up with both CD and vinyl decks.
Mixers have also come along way thanks to built-in audio processors, allowing the DJ to colour the sound with various effects such as phaser, flange and delays.
The next phase in this evolution is using software to control the way music is mixed. Software like Ableton and Traktor not only beat-matching but also has the ability to add effects without the need for expensive hardware (although a pro sound-card can be pretty hefty in price).
The debate is now wether this is DJ'ing or cheating at DJ'ing. The purists will still say that by removing the physical medium (the CD/vinyl itself) from the equation, the DJ has lost 'touch' with the sound and relies on software to handle the monkey-skill of matching two tempo's together. Another argument is that the mix is too perfect, leaving the natural drift of imperfect timing out of the mix.
By using software, the DJ now has greater scope to provide the audience with a more dynamic sound. Beat-matching becomes a single click and provides the time for the DJ to, in essence, create a remix on-the-fly. Not only can audio be stretched, looped or chopped up, the DJ also has the time to respond faster to the fickle response from the crowd. The detractors also say that the mixes can be pre-mixed, but that takes all the fun out off being a moment away from a train-wreck (a term used to describe two tracks being mixed together that arn't in sync)
More and more DJ's are making the transition, and with products like Final Scratch, the transition can be almost seamless (this technology allows vinyl DJ's to use a vinyl deck to manipulate audio from a PC). Technology is there to use to stretch our creative boundaries by allowing us to manipulate sound in new and interesting ways.