Google Co-op is a new way for content providers to create their own vertical search through a Google OneBox. Reading through the developer guide reminded me of the first time I saw Google Base — confusing. I'm sure that once I spend enough time with the documentation and experimenting with some code it will eventually make sense, but it's not as easy as they made it out to be.
Google Trends is really cool. As was said at the Press Day, they are basically giving users the keys to Google Zeitgeist. Since comparing things using this tool is extremely simple (use a comma) I can see a new breed of "Google Battles" about to make an appearance.
Google Notebook isn't quite ready yet, but from what I gather, it's basically a plugin that will follow you around from page to page. It acts as a convenient way to store and share important information from websites. From the webcast, it looked like they are using the same engine that is behind Google Pages in the full screen mode.
An upgrade to Google Desktop was also released. With this new version, you are able to use "gadgets" on your desktop or in your sidebar.
After the dust settled, it was an exciting day for Google. Google Co-op and the new Gadgets for Google Desktop should attract some developers that will likely create some pretty interesting things. It will be interesting to see what comes out of these new products. They say, even a 12 yr old can understand their Desktop API