The Web is Fluid
What's deep today may surface tomorrow
Even as we write, things are changing. Google has already partnered with existing library database providers to provide a searchable database of books in libraries. Take a look at the tutorials on Google Books if you want to know more.
But it will be a long, long, time (if ever) before a search engine can provide access to all the deep Web information out there. Savvy students understand that they can't find everything using Google or any other search engine. Most of the really good stuff is buried deep, and the library's databases are your gateway.