Finally 2012 brought 3 different sources of Frozen Yogurt to Zurich:
The number 1 of these 3 is
TYSON'S, located opposite the post office in Zurich Seefeld, Höschgasse 44. It's a combined shop/gallery that sells art, frozen yogurt with a large selection of excellent toppings and fresh fruits, a great combination of American/Swiss hotdogs with imported relishes and mustards, and it's also a video library with a fine selection of movies, many of them independent movies form all over the world.
The number 2 is
YOO-MOO, located opposite the Kaufleuten, Pelikanstrasse. Probably this shop was the very first to introduce froyo to Switzerland... Here you have the choice from three different handles/tastes and a large variety of different toppings.
The number 3 is
Lollipop, a sweets shop located in the Niederdorf.
For a judgment about the quality of the Frozen Yogurt you will have to visit all three of them - worthwile anyway if you a have a little time to find your best personal source...