Tagging but not the bad kind

I found the Youtube demo very useful - tagging is just uncontrolled subject headings for your own personal database. Would certainly be useful for people who use the internet a lot for their personal interests. My husband could probably use it for his aircraft modelling and I could use it for a database of recipes that have tags for all those ingredients that you want to use up from time to time - like the half a can of cocnut cream or the rest of a packet of risoni in the back of the cupboard. So thrifty! Not sure about library applications - have to think about that one some more.