There are some great ideas for digital storytelling activities over on the DS106 blog (I love Tom Woodward's suggestions for restrictions eg telling stories using only photos from a specific category).
They are very video and image – centric though so thought I'd speak up for text also amongst all the mashup mayhem. Obviously people have been doing storytelling online for ages, so we need to find new ways of doing it. One possibility would be tell a story through twitter. People have tried this before, some good examples in this post.
What I have in mind is not to actually use Twitter, but to create a story from a fictional set of tweets. It would be like Cloverfield in twitter. Or taking an existing movie and retelling it as if tweets from the character. What I like about this is the possibility for the story to emerge, and for the reader to know more than the characters. So is the twitter epistolary a possibility Mr Groom?