I think something that has happened around here more than once is that users mistake the lack of encouragement that a feature may provide for discouragement. It's a subtle different, but present. For instance, the tag system does not necessarily make it easy to find all easily-grouped content under a given header right now. However, I do not believe it discourages discovery. It just does not provide complete discovery nor does it encourage discovery of additional, potentially related tags.

I feel that the concern of improper tagging is alleviated by a) the editable community tag (although 2 of those might be cool) and b) the follow/share structure, as long as you have confidence in who you follow. I often feel "stuck" on tags. Sometimes I can't come up with one and sometimes I come up with four. While it's not ideal, and for instance "tag suggestions" that pop up might be nice, I don't think it's "broken." I don't like the idea of set categories that must be used, I do enjoy the flexibility of tags as they are currently.