I've been to two locations recently that have had Google Places stickers on the door. I wasn't sure if they'd been getting that much traction in the marketplace, so I asked the owners. Turns out, if you get a certain number of visits to your profile, Google will automatically send you one.
Reminds me of the early day so AdWords, when Google used to be very generous with swag to get the word out. Anyone have any traffic stats from Google Places they'd like to share?