It's one of the next things on our list ... which usually means that this feature will be coming within the next 1-2 months. There will be simple speed limits with voice alarming and also a interval timer.
@pod.runner: the latter feature you suggested is a bit difficult to handle - we're trying to make it not too difficult (everybody should be able to use this software even without a degree in Run.GPSiology)
This feature should include to set a range of speed e.g. 04:30 - 05:00 min/km or 04:40 +/- 00:10 min/km.
It would also be nice to set different intervals per km or minute.
In the meantime it would help to be able to set different time values for the different speech information e.g.
What do you think about adding limits to the measured speed and voice alarmling if going below or above the configured limits?
Same feature is in many heart rate monitors.