First, the setup. When you visit http://desktop.google.com/linux, you'll see a download link that leads you to two possibilities: an .rpm package for Red Hat / Fedora / Suse / Mandriva users, or a .deb package for Debian / Ubuntu folks. It's also possible to install Desktop Search from a repository: graphical installers for Ubuntu, Debian and openSUSE are all supported, along with command-line installation for APT, YUM, urpmi, YaST2, and RPM. Finally, if you want to get the source code to the project itself, Google states you can browse the Subversion repository for the project, although when I tried to do that I found nothing but empty directories (I suspect that's because I'm not a project member).
After I snagged the .deb installer package and saved it to my desktop, getting it installed was equally painless; I just ran the package manager, and then logged out and back in again. That part's required to allow the desktop components to load up. Again, as with Windows, a Google Desktop Search icon sits in the system tray (which in Ubuntu is at the top by default); you can double-click it to launch a search interface in a web browser or tap the Ctrl key twice to bring up a quick search box.
As with the other versions of Google Desktop Search, you access the vast majority of the program's settings through a Web browser, and you can also run searches from there. There's a lot of other functions that I haven't even gotten my feet wet with yet -- the file versioning, the integration with Gmail, and how the indexer handles things like metadata as well as file contents -- but I'll dig into those in the weeks to come. I'm dying to see how this thing copes with my 100GB of (legit) music files.