This is an interesting idea.
-Assign your own personal keywords(tags) to any web page.
-Search Shadows to easily find pages that you previously tagged as well as pages tagged by the shadows community.
-Make your tags searchable by the community or keep them totally private.
-Shadows harnesses the power of community and gives you tools to make your own search engine.
Unfortunately, I don't find the search page very intuitive. Nonetheless, it's a move in the right direction.
