As food and cuisine play an important part in Japanese culture and everyday life, there are many sites that resemble Yelp over here.
According to a study by Nielsen NetRatings Japan from February 2010, the biggest, in terms of reach, is Tabelog (http://tabelog.com/) with 12.4%.
Right behind that site is Gourmet Navigator (http://gnavi.co.jp/) with 12.1%.
3.: Yahoo Japan Gourmet: http://gourmet.yahoo.co.jp/ (8.3%)
4.: Foomoo by Hot Pepper, Inc.: http://www.hotpepper.jp/ (7.5%)
5.: Livedoor Gourmet: http://gourmet.livedoor.com/ (2.4%)