How Flickr and other web 2.0 tools can be used in the classroom?

Web 2.0 applications such as Flickr could be used for communication in the classroom between the teacher and parents.  Pictures of projects and activities done with class could be put on Flickr to share with parents.  Flickr could also be used for instructional purposes.  Photos of subjects relevant to the lesson could be posted and then could be accessed from the classroom computer for discussion and for a visual.  Other web 2.o applications could be used in order to show videos for demonstration purposes.  For example, a teacher could create a video on how to solve a particular math problem and upload it to an application where students would be able to access it from home in order to assist with homework.  Web 2.0 applications could also help students who are absent be able to see what homework they missed and view videos about how to do specific work.