Google already has two applications running under Linux: Picasa and Google Earth, but this is not enough for a company that uses Linux a lot.
In the presentation (PDF, eng) of the Linux Foundation Collaboration Summit, Google announced that they would release essential applications for the Linux desktop this year. Some of them will be open source and they will try to make support for major distributions.
Google applications that are not available to Linux users include: Google Talk, Google Desktop, SketchUp, Web Accelerator.