I used the free version of runkeeper on the Iphone last week. There's a setting for downhill skiing. It worked pretty well and give distance/speed etc. I've got a Garmin Forerunner as well which I'll try in a couple of weeks.
Try Sportsdo. I put it on my ipaq and it works well for skiing. You can upload your tracks to their website and overlay your days skiing onto Google Earth to see where you've been.
I've had some experience of Sportsdo, seems like a good application. When you set it skiing, it starts a new lap when it detects upward motion (on the lift). Clever stuff.