Bang on essay by Adam Rifkin about the differences in approach and culture between Google (Orkut, Wave, Buzz) and other recent social successes (Twitter, Foursquare, Facebook). Lots of good stuff here:
Google apps are for working and getting things done; social apps are for interacting and having fun.
Social apps offer a steady diet of junk food to keep us addicted; Google apps offer mostly bamboo.
Social apps are whimsical and fun; Google apps are whittled and functional.