Just a summary of a few of the better comments from this Voicethread:
1) literacy - collaborative story writing; sharing and reflection on writing; peer review and feedback; book reviews; with younger learners, picture book comments
2) foreign language learning - recitation and practice of pronunciation, commenting on a picture (focus on tense, fluency, or listening comprehension)
3) Thinking skills - brainstorming, problem-solving, word-problem solving (maths), critical thinking/reflection
4) distance education - contact with sick students/sick teacher
5) professional development - creation of presentations for promoting web 2.0 apps; use as an action research collaboration forum
I had the chance to see one of our classmates use this technology with a teacher in Taipei for fostering English language skills. The students were asked to plan a trip to a foreign country, including how they were going to get there, their travel plans, lodging, and potential problems they would face. They were asked to solve those problems and make a conclusion for their presentation. They presented in groups of two, using pictures from the internet and recording their voices for each slide. I listened to each presentation and provided detailed written feedback in terms of vocabulary, pronunciation, fluency, comprehension, and grammar. The teacher said that the students were excited and encouraged to have this kind of feedback and worked hard to finish their project and make recommended improvements. Their motivation and attitude of the project were both good. However, the authenticity of the final product was somewhat limited by the fact that their Voicethreads were private, for privacy concerns. Nevertheless, I see the benefit from this activity and hope that the example provides some insight.
I found a few on http://www.go2web20.net/ . You can try them and then post the ones that you think are useful for education or research.
Otherwise, think of a classroom problem (collaborating at home on group work, posting slideshows to the net, teaching about different cultures, or using Webquests for math) and then search out an app that can help with it.
Good lujck and keep up.