@Jagge: There is an online php-script which can do the job for you here - including sample input files (if you don't want to start off making your own algorithms at once):
http://www.mapmania.ch/amrd/index.php?show=amrd&la...
When you run the script, you get an example gpx-file out - I could upload a sample file, but I haven't got one handy just here.
Regarding usefulness of data, you can read about one use case here (Norwegian) - including a powepoint presentation,
http://sprint-camp.blogspot.com/2012/01/spennende-...
Here it was used to get a verification compared to the theory.
See also this sample where mapreading of different runners is compared:
http://3drerun.worldofo.com/2d/?analysis=1&anid=38
Here it is used to understand differences in technique, see problems with the technique of certain runners, etc.
Martin Lerjen has been working quite a lot with it - documented here (mostly in German),
http://o-zeugs.blogspot.com/search/label/Automated...
Several interesting use cases there in my opinion.
> And if it does not slow you down it doesn't matter that much either. And not
> reading enough or often enough is never reason for mistakes, just a symptom.
I think the most important tool is for the runner (and especially the coach) to understand and remember what really happened in the forest, and to compare performances. And also to understand the difference in technique compared to other runners who are more successful in certain parts of the terrain. But the technology is still quite young for me, so my thoughts might change along the way...