As a teaching tool, I have to say that Skype has been truly a change in how we can integrate not only other experts into our class (Lee Lowery had an author speak to her honors classes last year), but also allow us to teach using our technology directly.
I had the opportunity to teach someone how to use Sharepoint Designer over Skype. It was easy to begin a conversation and then use the tool to display my screen to them and let them ask me questions while I demonstrated personally how to do what they needed done. Though I have not had the opportunity to do this with any students yet, I have the feeling that within the next year I will have some of my web design students who would like to take advantage of this tool when they are finishing their large and complex projects.
The only concern I have for that is that we will be more attached to school time, so I imagine that some teachers will blur the lines even more between personal time and work time (an affliction that most teachers I know have).