EDIT: Demo up and running, the URL is http://videoapp.railsonedge.com/
Earlier this semester, I decided I wanted to keep working on my Video Application(see the Flash Video Tutorial). So when my databases teacher let us decide what our semester project would be, I signed up to do a YouTube-like site.
Since the tutorial, I've added a lot of things: User Authentication(authlogic), Video Thumbnails(using ffmpeg), Pagination(will_paginate), Tags/Tag Cloud(acts_as_taggable_on_steroids), and I wrote up some quick code to take care of user replies. I also added a little bit of CSS to the application so it didn't look so plain. It looks a lot better, but I'm still working on some of it. You can checkout the code for it on GitHub(http://github.com/balgarath/video-app/tree/master). The code from the previous tutorial is in the 'Tutorial' branch.
Anyway, I will have a demo of the application up sometime the next couple days. I'll get the URL posted here. Feel free to fork the repo and play around with the app.