There are now at least two iOS apps that allow you to DJ using Spotify - Pacemaker and djay.

Spotify logo

I find this really intriguing; I really like the idea of having such a huge catalogue to draw from. I also really like the idea of not having to manage/buy/own all the music I DJ with; being able to focus solely on selection, playlisting, curation, could be really liberating.

Note that it appears you need to be a Spotify Premium subscriber for this to work.

On the other hand, this could open the floodgates to "do you have youtube on there" requesters too ..