Jeanty @ Jacks on Sacramento Street in San Francisco does a very respectable beef tartare IMHO.

One to stay away from also IMHO is at a cafe called Dome on the north side of Rue St. Antoine, near St. Paul Metro stop, in the Marais in Paris. Similar to one of the posters above, I spent half of a 3 day long weekend from San Francisco to Paris on or within spitting distance of a loo a couple of years ago.