gritz, you are exactly right, flowers cannot be sent anonymously. The recipient also needs to be in your friends list at Facebook.
This would not 'asssit' stalking as the sender will never know the recipient's address and the recipient will not know the sender's address or personal information.
The recipient must also 'accept' the flowers by providing a delivery address (which will not be shared with the sender).
Regarding being smart with subject lines, we have tried to do that. Our subject line currently reads: Delivery of Fresh Flowers From [NAME_OF_SENDER] . We figured that putting the name of the sender will make the recipient more likley to give the email attention.
In addition to the recipient getting an email, the recipient also gets a 'notification' at Facebook. Both the email and the Facebook notification contain a link, which when clicked on, takes the recipient to a page at Social Flowers where they can provide a delivery address.
So far, conversions in terms of getting the recipient to provide a delivery address has not been a problem but we can always use more orders ;-)