We have mentioned Danny Sullivan's "Invisible Tabs" article from December 2003 several times here. Bill Slawski posted a new thread at Cre8asite Forums named Google and Invisible Tabs. In that thread he links to a recently released Google patent application named Interface for a universal search.
Bill explains that:
This patent application from Google, made public last week, goes on to describe alternatives to tabs, and varying ways to make different categories more prominent on a page, possibly based upon how relevant the search engine feels they may be to the query.
Update: Gary Price from SEW pointed out to me that the patent app was filed for less than a month after danny wrote his article. He also tells me to tell you guys that, "many companies have been doing work in what's called federated search for years. One interface to tap many databases." Some more related information at ResourceShelf.