Yeah, very interesting business. I think the option to post to a wall might be interesting. Part of giving a gift is the social gratitude that you have given a gift. Which is why these 'pay for virtual gift' apps in Facebook even exist and why people go as far as posting publicly rather than a message. It also makes the product very viral and would allow you to grow much faster, of course making message or wall post a choice.

Update: Thinking about it, not sure if it's possible as anyone could access your giftcard. If it is then it'd be interesting.