Gifts worth up to $100 do not require payment of duties.
To qualify, the shipping form has to show the contents and value, the purpose should be entered as "gift", It has to be from a private person to a private person (sender can't be a merchant), and the package should be marked with "unsolicited gift".
Enjoy your spontaneous gift giving.
Sender, in this case, is not defined as the originator of the gift as a concept, but from who the gift is physically shipped from....you can't send someone a gift via a merchant (e.g., purchase something as a gift and have the merchant ship it directly to the recipient...even if the gift recipient is yourself or a member of your address) to score the duty free benefit.
-Z