Ride defensively and make sure other trail users know you're there. Adjust your speed accordingly. If I see them wearing Ipods, I yell in my best "playground voice," "Passing on your LEFT."

I know some old gent cyclist who uses an AIR HORN around blind curves, and it works like a champ. I've been tempted to get one (be a great safety device too, for warding off dogs, perverts, etc).

I've seen a lot of unsafe behavior by other trail users, including other cyclists.