Google, I think, has been more kind to linux compared to other companies of the same gernre. When they released google-pack, linux users were quite disappointed, because it was available only for windows. However, they recently ported their software Picasa to linux. It uses WINE and mozilla. Google also made several patches for WINE in the process.
Google-talk is another software thats available only for windows. However, it uses the Jabber Protocol, which means that linux users can use Gaim or Kopete to chat. Later on, they made a web-interface built into GMail. The fact is, my friends who use windows prefer the web-interface over Google-Talk.
Google-Earth is available only for windows, but linux users can go to maps.google.com and have a look at satellite images. Maybe not as good as Google-earth, but heck, it works!
Google even has Special Search options, which includes a section on linux and BSD.
Recently, google started an online-calendar, and they are working on an online Spreadsheet. All you need is a web-browser, which means they'll work on any OS.