Google's Quick Search Box is a QuickSilver-like launcher that lets you search your computer for applications and data, as well as search the web, and your Google Apps accounts. I presume this will also eventually replace the search interface provided by Google Desktop. The project is in beta and is provided via the Labs.
From their blog:
One of our goals at Google is to make your search experience as fluid as possible. While much of our work is focused on Google.com, we're trying to make it just as easy to search outside your browser.
For the last year, we have been working on a new, open-source quick search box. Today, we are releasing our first developer preview for the Mac.
Via @factoryjoe