One of my absolute favorite things about living in San Diego is the abundance of frozen yogurt. Not only are frozen yogurt shops ubiquitous, they're unlike anything I've ever seen in my hometown in the Great White North, where Yogen Fruz is pretty much the only game in town.
There are two types of frozen yogurt shops in San Diego: self-serve and traditional (non self-serve). Both types of stores typically feature 10 or more flavors of frozen yogurt, ranging from classics like chocolate, peanut butter, and vanilla, plus a rotating selection of exotic and seasonal flavors. At self-serve stores, the machines are out in the open, which allows you to make a custom creation using as many different flavors and toppings as you want, then pay by the final weight (the going rate being 38¢/ounce). At traditional shops, the machines are behind the counter and they have pre-defined sizes. Though the options for toppings at both types of stores are similar (including fresh fruit, cookies, candy, and nuts), non self-serve stores charge per topping, which is somewhat limiting.
Ultimately, when I'm deciding which type of store to visit it comes down to whether I'm craving pure, unadulterated frozen yogurt, or a perfect storm of fruit, candy, and cookies, with some frozen yogurt thrown in for good measure.