My Take
I love Storybird! My students are hooked and we can't get enough of the great art. We use all the features, poems, short stories, and chapter books. I think one day they will allow students to upload their own art and that will really round out the tool. One way that I could also see it evolving is to give peer editing access in teacher classrooms. As the teacher, I would like to be able to assign stories to students for peer review.
How I Use It
I have used Storybird to help build writing skills in my classroom. Although students cannot add their art work (which is a common critique) I think it really helps stretch the student imagination to use their pictures to spark ideas. I enjoy watching student writing evolve as they move from paper to Storybird. The images enrich the student's stories and often entice them to write more!