I don't actually use very many web sites right now that implement tagging (in fact, del.icio.us might be the only one), but I've decided that a lot of other sites should be employing folksonomies.

For example, I'm working on my presentation for Thursday's Tech Summit about social bookmark services (with a long tangent into folksonomies and then tagging and libraries), and I really wish Microsoft's Clip Art Gallery would let users tag the images because Microsoft does a pretty lousy job of it on its own.