Social Media Marketing...what is it and who's using it?

Social Media Marketing is in our lives everyday and most of us don't even realize it.  How many times a day do you use your phone or computer to check your facebook or twitter?  For me its multiple times...an hour!  Social Media Marking has taken over our lives one tweet and status update at a time.  What we don't realize is how important Social Media Marketing is for companies especially because it's the easiest, not to mention free, form of advertising out there!  Many companies are looking to facebook, twitter and also youtube to keep customers informed and to get the attention of potential customers.  I couldn't even begin to tell you the number of times that I've noticed some organization or product that my friends "liked" on facebook.  With that kind of easy access to millions of people companies would be crazy not to take advantage of Social Media Marketing.  For a lot of local businesses sites like facebook are their main form of advertising and it's becoming the "word of mouth" of the social networking world that we live in. Based on some of the information I've found such as the feed back from a whole foods market I think the use of Social Media Marketing is very effective.  I found this article, http://smartblogs.com/socialmedia/2011/07/25/how-whole-foods-markets-uses-social-media-to-keep-its-marketing-fresh/, it discusses how this company uses websites such as twitter and how it benefits by keeping its customers and potential customers educated on their products by having most of its tweets be centered around customers questions.  It opens up a line of communication to people who actually consume their goods, which is important in the current competitive market place of today's economy.  Using social networking sites has its ups and downs with the potential to have negative feedback, but I feel that even the negative feedback can be used to the companies benefit if they take criticism constructively and are able to build and grow from it.   Here's some links that I've found relating to the topic of Social Media Marketing and also some short youtube to clips to help better understand this phenomenon.

http://thesocialcustomer.com/compukol/40463/social-media-marketing-defined

http://www.marketingpilgrim.com/2011/05/who-uses-social-media-an-infograph.html