Chiming in on this, I have always thought there could be value in aggregating tag data from every user and displaying the most relevant. I think a big problem with tagging is that users must remember to tag ahead of time. It's something you must do as you're making a post or reply. I think it's very robot-like behavior.

There is two problems:

1) Tagging can equate to higher interaction, therefore more tags is essentially always better. This creates an endless well of tags by design. Expect lots of tags. The question is how to handle them.

2) Tagging shouldn't be dependent on time of posting. 

Not sure what else to say about it but that's my two cents.