Microsoft has historically utilized the network effect to dominate the home computer market. As more people used Microsoft’s operating systems, more software was developed to run on those operating systems, which made more people buy Microsoft products. However, now that the internet makes software more universally accessible to computers running different operating systems, Google is taking the lead among technology companies in profiting from the network effect. Google refines its search techniques more effectively with every search performed; the improvement caused by every user attracts more users. As Google gets more popular the “experience effect” takes hold – searchers and advertisers continue to use Google more frequently because they are experienced with it.
Google also continue to attract advertisers in part because of the network effect. Because Google is a dominant search engine, companies attempt to tailor their sites so that they appear prominently in google searches. This creates a demand for website designers who can do this, which increases the number of websites molded to fit google searches.
However, the Google’s network effect is weaker than Microsoft’s because it is easy to switch to a different search engine without acquiring new software. This makes it an indirect network effect as opposed to Microsoft’s direct network effect.

http://www.nytimes.com/2008/07/07/technology/07google.html?scp=1&sq=network%20effect&st=cse