I just ate at the new Planet Sushi the other week (located at 860 Washington Ave in South Beach). It was a great addition to the neighborhood. They have restaurants in Paris and St. Tropez and this is their first U.S. location. The menu is pretty extensive! While it's not the place to go for authentic japanese, it was a good experience. The fish was fresh and the low prices allow you to order a bunch of different things to try. I really was impressed with their spicy tuna! And save room for the dessert sushi if you are a nutella fan.
their website is www.planetsushi.com although I can't figure out how to get the site translated to english - it's currently in french.