How do YOU acknowledge word-of-mouth referrals? How do you thank the referrer?

When someone thinks enough of you to refer one of their family or trusted friends, ignoring their kindness would be taken as an insult, while acknowledging their referral will encourage more referrals. It seems simple, but many dentists, surprisingly, just can’t figure out what to do.

What do you think of this idea?

A printed card is sent to the referring friend with a lottery ticket inside. The outside of the card says, “You’re worth a million to us.” On the inside where the ticket is attached, it is inscribed, “We hope you win.”
On the other inside flap there’s a personal note from the doctor, “Thank you for referring (patient) to us.”
Small cost, great value. I hope you can send 5 of these every day.