I had never thought of this before but that link is very good for folks who want to practice with the mechanics of editing/mixing for sure. At least the one I grabbed was wav files for all of the tracks of the project, live mics on many instruments so could play with panning, etc. too...
As I am light on the "final mix" (especially bussing) side of things, this was a lot of fun to see what I could do "quick" in X3. I grabbed the first project that caught my eye and imported all of the tracks into X3, did a little bus routing, inserted prochannels on the busses (many were default SONAR presets), tailored it a bit and mixed it down for kicks... (I actually only used ProChannel on the busses, so could have tweaked it significantly more, but chose not too).
and
then I listened to their mp3... X3 wins