I just finished reading an interesting article in Technology Review (What's next for Google) that's mostly about how Google has to start paying more attention to MS or risk being eaten, but what caught my eye was a neat table with the caption, "The searchable Internet (in red) contains only a fraction as much information as the various other forms of digital media." Or in other words, the invisible web.
I often stuggle to find relevant examples when explaining the invisible web to my students, and while students aren't necessarily searching for all the types of media represented in this table (maybe they will be by the end of the year!), it does do a really good job of showing the percentage of information that's not covered by Google (or search engine X). I like it.
Now technically, this media isn't currently all on the web, so maybe "invisible information" would be a better title, but I think it's safe to say someday most of it will be at least accessible from the web, and so I'm going to keep the graphic tucked away until I need it as an example :-)