I am well into a Voicethread project with a 4th grade class, and we all seem to be enjoying it. It's team teaching in the library for me and giving the kids a chance to learn some great technology while working on their voice in writing. Making the Simpsonized avatars was a hoot, and we are encouraging them to think of this book review as something for their peers instead of for their teachers. The conversation should be among them and not a traditional book report of setting, plot and theme--our goal is for them to say what they would say in person to a friend about why he or she should read the book. As a model, I made my own Voicethread digital book review of a favorite of mine, Mr. Putter and Tabby. Please note that it takes a minute to load.
A teacher sidenote--Voicethread is incredibly user-friendly and mine was done in minutes. The only trouble I had at first was finding out how to edit it (the little wheel in the left corner by the title).