Chris Anderson from Wired Magazine was recently on the Media Center Show and he mentioned that the long tail has been made possible by virtue of 3 factors:

Production has become easy for the general public.
Distribution now costs nothing (shelf space is a database entry).
Search is now very, very good and brings a geographically diverse audience to niche content.

The long tail is something I have been very interested in for many years but Chris' conversation about filters being the next most important aspect of making the long tail possible got me thinking. He mentioned that services like YouTube were still only showing part of the picture and that search engines like Google still showed what was popular rather than what was personally relevant. He suggested that a better, more personalized filter was needed.

Imagine a Personal Relevancy Engine that lived on the client-side instead of the server side. A smart agent that could have a meta view of your interests by tracking your clicks across websites, RSS feeds, documents you read and conversations you have and could help you discover and filter niche content by allowing you to:

Subscribe to sources you care about
Set rules for what's important
Get a heads-up-display while you work

I think that's a great idea. I will call it Touchstone ;)