If "x" is how much better Facebook was than MySpace, or how much better Google was than Yahoo search, then "x" is how much better you need to be than Yelp to beat Yelp.
Right now, it is debatable if you are even just better than Yelp.
I've spoken to numerous business owners in NYC who, after having turned down Yelp's super deluxe premier service^, begin to receive negative reviews that make no sense ("terrible service!" during a night the business was closed) or reference nonexistent items ("terrible apple pie!" for a bakery that doesn't offer apple pie).
^ Not the name, but they offer analytics and other services to businesses.
I guess I find Yelp's more in-depth reviews helpful for researching and planning, but too cumbersome for finding things to do on the fly.
Plus you can order food, reserve a table, see the menu, know if credit cards are accepted, if there's outside seating etc. just to name a few.