I have had my students collaborate with me via google apps both years I have taught. The students were required to write reflections on a project and send me the paper through google apps. My first year teaching since I was unfamiliar with it I did not know how to troubleshoot some of the issues my students had which was frustrating, but since I played with it more the next year it was much easier to navigate them throu issues.
I used google docs to collaborate with other math teachers when doing curriculum redesign last year as well, thus have shared and been shared on several files.
I had never used google forms before today. I hope to try to use this with my team when creating assessment so that it is a group effort rather than 1 of us making the assessment and then showing the other later.
I could also use google docs to have ongoing conversations with my students about current math topics, as well as a forum for students to ask each other questions!!