Years ago, I used Kid Writing in kindergarten. I really liked it, but this year I returned to kindergarten after using Lucy Calkins in first grade and wanted to try it out with kindergartners. The most useful thing for me was the curriculum plan that I purchased for $10 from Heinemann (the publisher of Units of Study). It really showed me how to adapt the program to kindergarten including some units that were not in the books. I had a great year. In some ways, it was easier for me than Kid Writing, because I do not feel that I have to make it around to every child as often. Also, I like the organization of different units.
Here is a link to the curriculular plan available from heinemann. Just take out the spaces.