Tags are great, but they can loose their meaning over time, especially when multiple people start using them. Why not add the ability to have a comment behind a tag to preserve the context / meaning? If you hover over the tag, the comment should pop up. This adds context to the tag.
e.g. I have a tag "Dead cold call". The meaning of this tag is: "A cold call confirmed as dead, and should never be invited again. We keep these contact records for networking, and to know we should not invite them to use our product again."