i dont know what the "truth" is as far as actual personal safety but i believe that sidewalk riding in urban settings discourages the non cycling public from taking cyclists seriously as vehicles who have a right to the road. we cyclists cant have it both ways. we either claim roads as ours to ride safely and with respect from other vehicles, or we can putter along at a "safe" 5mph on the sidewalk. does that mean you shouldnt ride onto a sidewalk to go half a block to the coffe shop? probably not (i usually will walk my bike in such a case but thats me) just remember those old ladys you are whizzing by and scaring the hell out of on the sidewalk will hop in their suvs and take it out on all of us trying to claim our rightful place in our city streets.