A lot of the ideas from these prototypes didn't make the cut: the blue search button that attracted too much attention, the blue background of the search results pages, showing separate sections for universal search results.
"We made hundreds of prototypes and gathered feedback from user studies, Googlers and through experiments — including one of our largest visible experiments ever. In the end, we came up with a design that provides dynamic, relevant search tools on the left, while lightening and updating the aesthetics all around," says Jon Wiley.
Even if the new interface is more cluttered with advanced options and I'll miss the dictionary links, I still think the redesign is an improvement. Google's search results pages look more consistent, the advanced options are more relevant and I already use them more often.
If you want to use the old interface, it's still available at http://www.google.com/webhp?hl=all. You can also try the Greasemonkey script "Hide Google Sidebar".