Via the New York Times, Wired's Playbook blog explains those blue lines on all the downhill snow courses at the Vancouver Olympics:â†µ
The idea is that the blue lines help skiers and boarders see the course more effectively. The lines on either side of the run visually link the gates and turns, while the lines across the course help the athletes with depth perception.â†µ
On the boarder cross course, the tops of the various terrain features are marked, so the riders can spot the landing areas.
They might not be the most scenic additions to the landscape, but skiiers and boarders crash often enough on their own without making things harder on them.