One aspect that has changed over the years is how information is consumed and shared. No company can live without it. Period. Whether it is industry information, competitor information, corporate news, employees’ personal knowledge and interests, etc. This is absolutely valuable to companies of all sizes – small or large. As the Intranets have failed, Enterprise Social Networks have become the only medium for employees to discover and share information. So, if it is only about information – yes, ESNs are effective and every company can find some value in it based on how many employees participate.
But, this does not mean every company needs tons of other features offered by Enterprise Social Networks. Most companies using Yammer, Jive and other products do not make good use of other features. It is still to be seen how much impact these ESNs bring to day-to-day employee workflows, which is a key aspect of this question.