Two suggestions in one.
I like to be able to search for workouts with certain tracks / artists associated to them. For example a search for 'Razorlight' would bring up a list of workouts that I have access to where the user has listed to at least one song by Razorlight during the workout.
I also would like to be able to trigger this search from my workouts. For example I look at one on my previous workouts, see a track by Snow Patrol and click on that text to find other members who have listened to that song/any song by Snow Patrol.
Why? It is interesting to see who runs/cycles/walks near to you (by looking on the map) equally it will be interesting to see who runs/cycles/walks near to you (near by musical tastes!)