I think what's neat about this guy's approach is he's morphed subreddits into a fully complemented, distributed algebra by letting you take intersections and unions of different "subcategories" of discussion.

I suppose one could could argue "isn't any interface with tagging basically doing this?" To be fair, del.icio.us and the like usually let you combine tags in some way, but none of them get out of your way enough or have sufficiently simple voting mechanisms to be a really nice way to grok news. None of them implement a nice comment system, either.

This is like having your cake and eating it too! If only I didn't have to register an account to comment...