I recently came across a web-based service called Vialogues which allows you to upload a video, or use one posted to YouTube, to start a discussion. Video + Dialogue = Vialogue!
As an alternative to a text-based forum or bulletin board, it seems to me that the potential is exciting. Once you have created an account on the website, you can upload a video and start a vialogue. You could get students to use the site directly to comment on your video input, or could grab some code from the site to embed in your class Moodle page or other web-page. Students could then view comments and post their own replies from that page.
Here is a vialogue that I created to give you a flavour of how it works.
All in all, it seems to me that this is a web-service well worth exploring in the classroom, and I am itching to find a project I can try it out with!