This site has an ambitious project going wanting to list all sushi restaurants in the world! They rely on the participation of its readers to keep the listings complete and up-to-date. They use web-based forms to submit and update information about sushi restaurants, and also to submit peoples opinions and reviews about listed restaurants. They say that the Reference currently lists 3,162 open restaurants at 3,357 different locations! Quite impressive! The site started in 1994, but you can also see that it has some problems keeping it up. Several of the locations in Oslo does not not exist anymore for instance. I will send them an update on this. So - if you are looking for something in your neighborhood or want to update with your info, you should check out this site.

Link:
The World-Wide Sushi Restaurant Reference