Valve have today announced changes to the way Steam gifts work to improve the trading experience.
The changes that have come into affect mean that if you buy a game as a gift and keep it in your inventory, you won't be able to trade the game for thirty days. This doesn't change how things work when passing the gift to a user as normal though, you can still do that straight away.
According to the Steam community post, the change has come about so that people can't trade you a gift and then cancel the transaction. This would previously cause the guy receiving the game to lose it.
Valve said that they have done this to give a "better experience" when trading gifts.
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.
This has obviously been put in place to stop individuals who do trade scams for games and what not. It is nice to see Valve are putting a stop to this and it shouldn't really affect those that do it legitimately.