For restaurants, I've had a good experience with OpenTable's and Zagat's ratings. Both are consistently reliable -- no nasty surprises so far. (FWIW, the best way to access OpenTable reviews is to search for a reservation in a particular area, and then sort by the number of stars.)

For bars and the like, I've had a good experience with Zagat's specialty guides -- e.g., http://www.zagat.com/product/specialty-guides/san-francisco-...