Since Google Base was discovered, there have been many guesses as to what it will be and do. Theories range anywhere from an eBay killer to an all encompassing "megabase" of useful and relevant information for any and all purposes. I would like to offer you my opinion as to what might be happening behind the walls at the Googleplex.
Google is smart, they know what they want, and more importantly they know what people want. The answer to both is "information" and "money". Looking at both of these "wants", they must decide how they can do this and stick to their "do no evil" guns.
Allowing people to physically store searchable information on Google's servers rather than Google having to crawl the web for everything is a very smart idea. A system where people can upload information will let Google extend past the previous boundaries of the "You are not logged in" problem that GoogleBot has no doubt experienced. There is a whole lot of information behind log-in screens, and Google wouldn't be Google if it didn't want to organize the world's information and make it universally accessible and useful.
Lots of information behind log-in screens is "paid" content that is not accessible to people or search engines for a reason. Some information is meant to be private, and some is meant to make money. In either case, it should not be made freely available to just anybody.
Here's what I suspect is happening: People want to make money, so Google will let them. Information stored in the Google Base will obviously be searchable, but I would also wager that it will resemble the "Google Print" product where information is only partially available to searchers at the publisher's request. There is no question this part of the service will be completely free.
Not much different than the "pay us and we will let you in" model, publishers will earn money from searchers who want information. Of course the price will be up to the publisher, anywhere from free to big bucks.
Not only text information will be stored in the Google Base; other things such as images, videos (replacing the video Upload tool), e-books, downloadable software and music will probably also be available.
Google wants money too. Every item that is purchased from the Google Base will put a percentage of that sale directly into their pocket. The piece of the puzzle that makes everything here possible is Google Purchases. It will definitely be a part of this project, helping the selling and purchasing of data become reality.