Last summer, my hometown experienced a sudden sharrow explosion, as an influx of federal stimulus money was used in part to paste them en masse on an extensive network of low-traffic, neighborhood streets in our northeast quadrant. Laid out smack in the middle of the road, they're meant to show all road users where people on bikes can ride most safely -- but in practice their main usefulness has been to map out bikeable routes across town.
also, the article sites the cost @ $229 per sharrow. Seems like a cheap way to bring awareness to certain routes.
Jim