Steam Trading is a Changin'

Want to trade games? You better plan ahead; there's now a 30 day wait period between time of purchase and tradability in an effort to deter fraudulent resellers.

From the announcement:

All new games purchased as a gift and placed in the purchaser's inventory will be untradable for 30 days. The gift may still be gifted at any time. The only change is to trading.

We've made this change to make trading gifts a better experience for those receiving the gifts. We're hoping this lowers the number of people who trade for a game only to have the game revoked later due to issues with the purchaser's payment method.

A thirty day wait period makes sense by this logic, but it sure has messed up my holiday trading. But don't worry, any gifting you're planning to do out of the kindness of your heart remains intact.