Google desktop has now been made available for Linux
You can peruse the documentation or download the files from the Linux version of the site.
As should be expected there are both RPM versions (RedHat and derivatives) and .debs (for Ubuntu / Debian).
I'm not sure how useful this would be, as the only time I need to conduct search is with email and thunderbird handles that really well (and quickly too!).
Of course the problem with a Google bit of software on a machine running Linux could be the license.
While the software may use some open source libraries it's not open source itself