I just made a kiwi slush in the blender and it's icy and refreshing...and a little on the tart side (which I like). I just modified the Kiwi Margarita recipe at the bottom of this page. Here's the recipe:
2 kiwis, peeled
juice of 1/2 a lime
8 ice cubes
1 tablespoon sugar (more if it's too tart for you)
1/2 cup water
Whirl in a blender until super smooth.