Skills

Assassin

• Fox Fangs (PvP): reduced bonus damage to 10…25.
• Leaping Mantis Sting: reduced bonus damage to 5…15.

Dervish

• Crippling Victory: increased adrenaline cost to 6; removed Cripple from AoE component.
• Onslaught (PvP): removed 25% movement-speed increase.
• Twin Moon Sweep (PvP): reduced damage by 25%.
• Wearying Strike: increase adrenaline cost to 6.

Elementalist

• Blinding Flash: increased recharge to 8 seconds.
• Glyph of Sacrifice: added the following functionality: "Ends prematurely if you use a non-spell skill."
• Obsidian Flame (PvP): split for PvP; reduced damage to 22…92.

Monk

• Shield Guardian: reduced cost to 5 Energy; increased casting time to 1.5 seconds.
• Spirit Bond: reduced healing threshold to 50 damage; reduced healing to 30…90.
• Spirit Bond (PvP): reduced healing threshold to 50 damage; reduced healing to 30…90.

Paragon

• Wild Throw: added the following functionality: "All of your non-spear attack skills are disabled for 3 seconds."

Ranger

• Melandru's Shot: reduced recharge to 8 seconds.

Warrior

• Enraged Smash (PvP): split for PvP; increased recharge to 10 seconds.
• Yeti Smash: removed 1 second activation; reduced adrenaline cost to 6.

Guild Wars Wiki notes

• This update was explained on Feedback:Robert Gee/Journal#January 20th 2012: Snow Day Skill Update Preview.