Well, sometimes the sidewalk is faster... When there aren't many pedestrians but there is a traffic jam... one ways... light is red and you want to turn right...
Here in Hungary, you must ride on the road, too, unless it's "unfit" for biking, in which case you're allowed to ride on the sidewalk, but without getting in the way of pedestrians and at 6mi/h max. Ridiculous! Theoretically, that means 4 year-olds with their training wheels and beginners who can't kep a straight line are supposed to ride in the 30-40 mi/h traffic. And lately F'ing policemen have been known to fine bikers for using the sidewalk. B@stards.
Generally, though, bikers ride wherever they feel like and police couldn't care less.