I'm quite new to hubski, and I think that it very refreshing to see such an experiment in online communities. Segmenting (well, organizing) posts is definitely a hard problem.

There is an interesting discussion in SE Podcast #43 between Alexis Ohanian (Reddit) and Joel Spolsky (Stack Exchange) on how they tackled this in their products. At an early stage, Reddit hesitated between tags and separate communities:

http://blog.stackoverflow.com/2013/02/podcast-43-false-facts.../