I buy the 32oz size plain nonfat yogurt when it is on sale. When I get home I portion it out into ice cube trays and freeze it. After the yogurt is frozen I place them in a freezer bag and store them for later use.
Later on when I want to make a smoothie or ice cream I add the cubes instead of ice. Not only does it helps to make a smoother product but it keeps it from being water down.