Not sure how many are on Facebook - but here is an offer from World Caching Store that was just posted today -
"World Caching StoreNEW Fans ( Like) will receive a nano cache FREE.
If you are already a fan, get a friend to be a fan and will still send you a free nano cache ... and one to your friend as well !
Send us an email to email@example.com with your "new fan" note and an address and we will get that nano off to you !"
They did send an email which said it was limited to the first 50 - but who knows.