I think that you need to encourage more people to move away from thinking this as a Reddit clone. Tags are basically subreddits, and are doomed to run into the same problems. It seems like the user-follow feature is way more interesting and deep than the subject-following feature. I would do everything I could to encourage following users over following tags- but I think you already know that.

It would be great if you could make your own groups of people you're following. For instance, I could look at my followees (who I'm following) and create X number of categories (say a dozen per user) and sort my followees into those categories. Then if I want to filter by my own categories, I can see the users I follow for their programming acumen, humor, writing quality, or what have you. Whatever actually drew me to the user in the first place.

Also, while I'm replying to you, has anyone mentioned yet that it's very hard to read the dark blue text when you're following someone but they're not following you? I imagine you don't see a lot of people not following you, so it might not seem like much of an issue, but for me, at least, I have to highlight the user name to be sure of who I'm looking at.