In October 2012, Facebook made a change to its news feed algorithm that appeared to dramatically reduce the number of posts a user would see from pages they had liked. At the same time, Facebook launched a new, for-pay, feature called "promoted posts."
Richard Metzger penned a widely read blog post on Dangerous Minds challenging the ethics of the change, which he argued in essence took a feature (post reach) that he and other pages had previously enjoyed as free...and turned it into a for-pay feature.
Twitter user Leonard Barshack who had gone by the Twitter handle @sunvalley for several years, sued the company when it suddenly seized the handle and gave it to the Sun Valley corporation. Twitter cited its terms of service as prohibiting anyone from "impersonating" a person or company. Barshack adamantly insisted he was never impersonating anyone, but Twitter's TOS allowed them to take back the handle without warning.
Instagram set off an even bigger firestorm in December 2012 after announcing a change to its TOS that suggested the company might claim ownership of images published to the social platform. After a social media furor, and the cancellation of accounts by some major users including National Geographic Magazine, the company withdrew the changes and reverted to its previous TOS.
Incidents like these have led to discussions about the need for a People's Terms of Service - something akin to a 'negotiated contract' between user and provider, a more equitable balance of terms between sharing and protecting data, consistent with the long history of contract law between parties. Has social media reached the stage where it is time for a negotiated exchange, a People's TOS?
For more on these examples, see Santa Clara University's excellent article: Clicking Through to the Ethics of Social Media Terms of Service