The strength of social media is that it can answer questions you had not asked and perhaps had not even thought of. Its weakness is that it can't answer most of the questions that market researchers' clients ask. There have been some successes and a couple of examples are

• Assessing campaign or message breaks through.

• Identifying language, topics and ideas.

• Outside market research.

But the key problems are:

• Most people do not comment in social media, and most of the comments are not about clients’ brands and services.

• Social media deals with the world as it is, brands can’t use it to test ads, to test new products and services, or almost any future plan.

• The dynamic quality of social media means that it is very difficult to compare two activities. Thus the accuracy of social media measurements become limited.

• Good social media usage requires people, which tend to make it more expensive and slower.

• It is very difficult to attribute the comments to distinct groups.

Read more at: 

http://www.greenbookblog.org/2014/04/25/why-has-social-media-analytics-met-with-limited-success-in-market-research/</a