Social Media Networks and Marketing
Social Media Networks (SMN) and Social Media Optimization (SMO) are the two common terms about social media.
The SMN's is the networks that depends on the users to build its content, the samples of these networks is Social Sites (Facebook and linkedIn), micro blogging (Twitter) ,Blogs (BlogSpot), Videos (Youtube) and there are 150+ social networks [I know all 
], all these sites share the same approach: "Users Build the Content and Connect with Others".
About the SMO:
let's first define the "Marketing" : the simple definition is "How to build long-term,stable, profitable relationship between your organization(you) and your customers(friends) to create and capture values for all parties", so the SMO is an online marketing tool aims to use social media networks to connect with your customers and friends, Also SMO is how to use the power of "a work of Mouth", you can recommend a book on twitter by words, you can submit bad news about a company, these words can affect the long-term relationship between reader and writer, between the Client and company.
Sample of Using SMO in Egypt
Etisalat-Misr Built a Facebook Application for Customer Support
Etisalat,Vodafone,Mobinil has twitter accounts, Youtube Channels
Most Egyptian professionals now on LinkedIn
Many Companies has twitter account to post their updated news
All these activities focus on "How to maintain the relation between you and your customers and friends "
I am working in Digital Marketing Since 2004 by email campaigns,Search Engine Optimization, analytics and other tools, now the hero of Digital Marketing is SMO