How Can I Use Postcards for Promotion?

In participating in Jennifer Chiaverini's postcard promotion for her last book and hearing about her  postcard/pin pal promotion for Sonoma Rose, I began to wonder how I can further use my postcards for Tales of Adventure & Discovery (a children's anthology of poems and stories).  I had them printed when the book was published and have been using them ever since.

Send postcards when announcing events.
Send postcards when writing to friends and colleagues.
Pass them out at book signings.
Give to friends to send out, along with a small gift, as Jennifer does with her pins.
Include them with a book purchase.

I'm trying to discover some new and creative ways to further use these postcards.

More Postcard Promotion the Jennifer Chiaverini Way

Jennifer Chiaverini is promoting her next book, Sonoma Rose, with her "postcard and pin pal" technique.  I participated in the promotion for her last book, but didn't hear about this one until after her quota of readers signed up.

For distributing the postcards Jennifer sends them, each volunteer receives a limited edition Sonoma Rose pin.  This certainly is a fun way to promote...for the author and the volunteers.

Jennifer is author of the Elm Creek Quilts series.

Do you promote with postcards?  Do you have any interesting techniques for distributing them?