http://store.steampowered.com/news/4816/
Some of the achievements have already been added, and some are even already achievable:
http://steamtreasurehunt.wikia.com/wiki/Winter_Objectives
I'm not sure where this info came from (possibly translation server), so it might not be completely legit. But I've seen it posted around, and it seems believable:
"How to enter:
Entries will be based
on the number of coal
remaining in your
Steam Inventory on
January 2nd at 10am
PST."
"You must also have 10
items on your Steam
wishlist at that time to
qualify"
"Click here for complete
contest rules."
Grand Prize
1 winner
Every single game on Steam
First Prize
50 winners
Top 10 items on wishlist
Second Prize
100 winners
Top 5 items on wishlist
Third Prize
1,000 winners
Valve Complete Pack
-------------------
Gifts
Congratulations! You got a gift.
Here is what you can do with it:
Use it
"The Great Gift Pile has both full games
and coupons. You can simply use them."
Trade it
"You can trade both gifts and coal with your friends
for all kinds of things. Steam Trading makes this easy."
Give it
"Feeling generous? Send your
gift to a friend, or give it to a
stranger. Just image the
karma!"
Coal
"You got a lump of coal? Don't despair.
Here are three things you can do with it:"
Craft it
"Seven pieces of coal can be crafted into
a gift from the Gift Pile. Don't worry, you
won't get coal again."
Save it
"Or you can save it all up. Each lump of
coal is an entry into the Epic Holiday
Giveaway on January 2."
--
Ginhyun
I dig my hole, you build a wall