I love NST (great work team!) and have a couple of suggestions to hopefully make it even better:
1) There needs to be a way to pause a workout across runs of the NST (which might be across power downs of the device). That is, if you save a workout (or close NST, or power down the device) with it paused, then when you load it again you should have the option of resuming from where you left off.
This is important (for example) for people whose cycle journeys exceed the battery life of their device, and who carry a spare battery that they need to pop in without ending their workout in NST. It might also be useful to people doing multi-day activities who want the end result to appear as one workout.
2) I regularly forget to resume my workout after I paused it for a while (eg. stop and have a coffee during my bike ride). I usually remember a few minutes after I've resumed the journey. This will cause NST to calculate a ridiculously high speed to the point at which I resumed the workout (for example, my last bike ride supposedly had a max speed of 120kph!).. It could easily handle this by offering to add the time that has elapsed since your position started to change.
3) Related to the above, I don't use auto-pausing because GPS errors cause spikes in instantaneous speed when motionless, which exceed valid (low) speeds when not officially paused, so it's not possible to set a good threshhold. I feel that auto-paused sensing would be better done by position rather than speed. Though motionless GPS position jitters too, it should be relatively easy to spot that and conclude that the device is in fact actually motionless and the workout should then be (after a configurable amount of time) auto-paused. Similar thing again for auto-resume. Or maybe you're paused when you pause the music!
4) PLEASE PLEASE PLEASE use the might of the Nokia name to persuade a cycle computer manufacturer to integrate with your devices by bluetooth, so that NST can have speed, distance and (more importantly, since it's not available from GPS) cadence direct from the bike equipment. Though you could actually measure cadence (pedal rotations per min) using the accelerometer if the device is strapped to your thigh!