It's situations like that which have led to numerous scandals on the Internet, such as the most recent PR issue surrounding Facebook. If you recall, their terms of service were changed on the fly and resulted in a massive uproar, ultimately ending in the company backtracking.
Unlike Facebook, however, most companies aren't interested in letting users dictate their terms of service. It is for that very reason the EFF thinks there is a need for people to be more aware of changes in services they use, and have built an infrastructure to do just that. Their recently launched “terms of service tracker” at TOSBack.org will let people see up to date changes in terms of service agreements. Currently tracking many popular companies like Google, Facebook, YouTube, eBay and others, the EFF hopes it will encourage people to be more aware of what they agree to when they create or maintain an account at any of these sites.