I'm guessing the entire system only supports 3 tags total, amirite?

No, we could have 80 tags if we wanted to. Actually, the second tags still reside in the data.

You can still keep the second tag with this new system though. My question is why in the world did you want to get rid of the second tag?

There were a few reasons. The most concise are: 1) tags could then have between 0-5 tags, and 4 of the tags would be repetitive. You can see that elsewhere in this post, one of the biggest complaints is the feeling of clutter. Having two primary and two corresponding personal tags was a mess. 2) Community tags were on just over 5% of posts, and they were very rarely edited.

We feel, and others have told us, that the community tags and personal tags are good ideas, but they were poorly executed. With this current approach, we simplify the functionality overall, and ramp up the utility of both of those functions.

Being a new user that hasn't fully developed a network of users to rely on, I'm not sure that I can anymore with this system. We'll see, though.

Give it a shot. Like I said, this is an experiment. Often what we learn from these experiments leads us to something we never could have never planned out in any number of discussions. In experimentation, I have found the personal tag to be a compelling content discovery tool.

One thing I have also considered is how this plays into scaling. The conventional wisdom says that as tags grow more popular, the ratio of quality content will fall. However, what if I really want to get great #politics posts even after hundreds of users are submitting to it? Previously, I would have had to follow #politics, and filter an ever-increasingly large swath of users (in entirety, not just their politics posts) to cull out the chaff. It is a race, that eventually I would lose. Now, I have the option to browse #politics, find the best users submitting to it, and follow their personal politics tags. With this approach, my politics feed doesn't degrade over time. Of course, I need to work if I want new voices, but I won't have to be constantly filtering users to have a quality politics feed.

Of course, for quieter tags, I can take the opposite approach: filtering a personal tag or two might be all it takes to keep the overall tag quality, and I need't filter out those users wholesale. In that respect, we now have two kinds of filtering: content-specific, and user-specific.