Such cards are widely used for dance and theatre performance promotion here
in Auckland, New Zealand. They're not free, by any means, but are
relatively inexpensive (compared to newspaper advertising) and seem to be
pretty effective for direct selling/targeted promotion - placed in cafes,
galleries, bookstores, campus drop off places, theatre counters and so on,
and mailed to your mailing list and target audience members.
-Raewyn