Pardon my rant, please ...
Unless someone starts marking these trails as "Hiking Only" or something to that effect, then enforcing this rule, they are free to all to use as they please.
I must respectfully -- but vigorously -- disagree with this statement, especially the "to use as they please" part. Neither skiers nor hikers (nor anyone else) are free to use shared trails strictly as they please.
All are under considerable social, if not legal obligation to be very aware of the impact their own activity has on others and adjust their behavior accordingly. That impact includes the threats their activity may pose to safety, especially the safety of others. All have an obligation to behave responsibly so as to minmize those threats. Common sense dictates that the greater the safety threat your activity poses, the heavier your burden of obligation. Period.
The situation becomes particularly acute on narrow trails (no maneuvering room) with short sight distances and blind spots. Under those conditions it is irresponsible to the point of being reckless or outright negligent to ski, sled, snowboard, glissade or butt-slide downhill in a manner that exceeds one's capacity to literally stop or veer away on a dime in order to avoid a collision with another trail user. No if, ands or buts about it. It is your responsibility alone to always be in control.
Likewise, it is both supremely foolish and irresponsible for a slower moving user to obstinately refuse to give "track" if he sees the other guy bearing down on him and has a safe chance to get out of the way.
... you should have had plenty of warning someone was coming down the mountain ahead of you. Its not like skiers come down silently with the brushing aside of snow.
Sorry, but this is quite wrong, also.
Now, I have no particular sympathy for iPod users who block out the sounds of the world (by replacing them with other noise) as they walk. They are acting somewhat irresponsibly, I think, by impairing one of their senses. On the other hand, I suspect a lot of hikers (and skiers, etc.) are, like myself, naturally hearing impaired to one degree or another. So the noise skiers make -- whether it be the natural sound of their slats on snow or their shouts of warning or exuberant "whoopeeeees" -- is not sufficient to warn and protect me by avoiding collisions with them. At the least, I need good visual clues.
The old rule with visual warnings is this: If you can't make eye contact with the other guy, never assume he sees you and knows you are there.
G.