I used the GPS with My Tracks on my HTC Magic for my final ride of last season. I found it was a really good record of how long I actually boarded for and the maximum speed I got up to, as well as other stats. Sadly, my phone ran out of battery on my last run, but I'm looking forward to using it again next time, and I'll definitely get an extra battery to swap during the day.
One thing I liked was the fact that I could zoom in and compare the different paths I took going down the same mountain. In some places, I was making the exact same turns each time, without realising it. Now I know to mix it up next time so I can improve.
Looking at your picture, SnowtoriousBIG, do the different colours indicate the speeds you were going at the part of the run?