One of the few tools where it's quite fun just to search to see what results you get back. The enjoyment comes, I think, because of the context. It links things like place names or people with documents. It not only works across their document set but also other open archives. This gives interesting results like who had classical Greek names in the American Civil War.
The "dynamic clustering" is alright in that it finds similar documents by phrases appearing in the document. As names are also given similarities such as "hercules" and "herakles". It doesn't work so well for "io" getting very weird results. Searching on "hecuba" for example doesn't find "Agamemnnon" or "Odysseus" but finds "hector" and "priam".
Open Archives Initiative:
London over 400 years (a shame there's no Quicktime panoramas for the 1600s):