I did have a good look at Gills tracking at Zandvoort and was suprised how often Matts course changed whilst running back up the course towards Zandvoort compared to Gills. Then I remembered Gill was flying a kite and I beleive Matt had a problem and thus sailed the long run under main and jib alone.
I would also agree that GPS isn't that useful a tool when it comes down to a training aid...meaning it's best used for navigational purposes but the fact that it can re-call certain data as described above can help understand where gains and losses have been made but only by comparison.