Google Buzz, an odd social networking feature in Gmail, strove to take on Facebook and Twitter but failed, except in its influence on Google+. Integration with Picasa, Flickr, Google Reader, YouTube, Blogger, and Twitter presaged the let's-dump-everything-here tendency of more recent aggregators. Buzz lasted 20 months.
If you were a programmer back then, you probably remember the demise of Code Search, the remarkable attempt to make open source code more accessible, no matter where it resides. Ohloh has taken up the mantle.
Google bought Jaiku, a Twitter-like networking service, in 2007, stopped new development in 2009, and finally gave up the ghost in 2011, as tweets overwhelmed jaiks. iGoogle, which features prominently in the July 2012 spring-cleaning announcement, lost its social features.