Here is Hippalus with the details:
"Due to popular demand, we have extended the availability of the gifting feature in the Store through the end of Snowdown Showdown on January 6. Only summoners that were on your Friend list at the start of the Snowdown event can be gifted. Snowdown summoner icons will continue to be rewarded for your first gift of RP, a champion, or a skin.
We hope to bring gifting back permanently in 2013 once we have evaluated its impact on account fraud and hacking, and taken any necessary additional steps to protect your accounts."
