Chris and I had been arguing about the nature of tagging. He believes that tagging should be an activity that's private. He never looks at tags that other people have. I'm more on the side that tagging is an activity that's public. The fact that you have thousands of people labeling things, there will be some overlap in calling it the same thing. In that way, you can find other related things.
I think I just realized the main difference between our philosophies is what type of keywords that we think we would employ. If the tags that you put on an object are intrinsic properties of the object, then there's no problem that it is public. However, if the tags that you put on an object are properties of how it related to you, then that's how they could be seen as private.