I personally think, indexing visiting web pages is helpful; especially to folk like me, students. We browse the net, read new stuff around and then somewhere down the road we come across with something and we know that I saw something related on some webpage
that I visited, but not remembering its URL; now using Google Desktop Search, it’s easy.
I wish MSN guys add it too, and also, just like what they have done that searching something on Google.com also shows the results of desktop (including visited pages). Adding these two I will definitely uninstall Google toolbar and desktop search J
Using indexing service as backend is nice, one can create custom filters for new formats, its super cool; to have some nice UI for indexing service.