My two cents; While redditors love to follow tags as a "replacement" for subreddits, the subreddit system is ultimately something that should stay on reddit. Hubski revolves around following users who submit content that you find interesting, not creating communities that you follow, regardless of who is doing the posting. One of the biggest issues on reddit is the inability to escape image macros, memes, and cat images because they have inevitably invaded every subreddit. With a system where you follow users, you have the choice to not see things you don't want to. The tags are still a great way to enhance and organize the content and find things that are relevant to your interests, but following the users who submit said content is ultimately how hubski works.