Social Media Marketing is getting very popular among marketers these days. This makes a complete sense to me as it is the best way to ensure your presence to the world. If you check the Alexa of top sites globally (in terms of traffic), you will find many social networking sites are among the top sites list, making them an excellent way to drive traffic to your site. Many companies including some big brands have understood the importance of social media marketing and are using it to their benefit, as these sites are becoming one of the best way to reach large number of potential customers. Examples of social media sites are Facebook, Twitter, Digg, Mixx, Reddit etc
Coca Cola
Blog: Coca-Cola Conversations
Facebook Application: Sprite Sips and Coke Tag
Virtual Worlds (Second life): Virtual Thirst
Dell
Blog: Direct2Dell, Nine official internal blogs
Microblogging: Twitter - 22 corporate accounts
Virtual Worlds: Second Life Island
KFC
Blog: KFC Nation Citizen Blogs
Social networks: KFC Nation
Facebook: fan page
National Geographic
Blog: The Green Guide
Forums: NGC Forums
Microblogging: Twitter account
Online Video: YouTube channel, Everyday Explorer
Social networks: MySpace, Imbee
Not sure it's exactly interesting, the power of social media has been well established for a few years now (especially with the buzz surrounding places like Twitter), it's probably the fastest growing area of marketing (currently), though I would point out your use of Alexia is a poor method of determining traffic as it is well known that Alexia only measures through a very small minority of web visitors therefore suffers at the extent of it's own inferiority.
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