Visual folksonomy explanation

After reading Thomas's folksonomy explanations this morning, I came up with this diagram to show the differences between tagging approaches:

On the vertical axis, we have tags and whether they are public or private. On the horizontal axis, we have the stuff you would tag in these systems (either yours, other people's, or a mixture). Flickr sits in the middle since it allows you to tag your contacts' photos as well as your own, and to keep some photos (and presumably tags) private. Del.icio.us, of course, lets you tag your own stuff if you want to. I put Furl in the lower right quadrant because it seems to be the only system that lets you keep private tags of others' stuff (properly, it should be closer to Flickr).