The other day I tried out Ableton Live for the first time. I found some tracks and just added them and tried to do some easy mixes. As I went through the different tracks I found that I had added an old track that is not played on click (Tempo is all over the place).
However... When I tried it out the beats matched perfectly! I was stunned about how good the timestretch in the software was.
Ean did a tutorial on how to edit old tracks so they can be played in sync with other tracks in Traktor.
A very good way to get old tracks into your sets.