OMG Livejournal tags!!!
Does the size of the font indicate how popular a given tag is, or something like that?
If you look at what people are tagging, it is their own interests rather than blog post contents. LiveJournal has had this feature, as well as being able to search for other people with similar interests to you, for as long as I can remember. At least 4 years.
Tagging interests also applies to communities too.
The visualization about which interests are popular is new though.