So, basically, there's a trigger, you know, when you change the functionality of the site without warning everyone. That's a bad idea, it causes people to not like the site anymore. While us youngins are supposed to be ok with change, the truth is that we get used to things, and when they change without warning, without input, we hate it. We like to know WHY things are being done the way they are, this should not be a surprise for anyone who deals with the under 25 crowd on a regular basis.
After the trigger event, people use the easiest resource available to them to communicate this dislike, be it the forums, or comments or the 'contact us' button. Of course, the more media or photosphere attention is received, the bigger the revolt. The Facebook change to the terms and conditions got onto the news, and it exploded. If the news hadn't reported it, it might not have gotten to be the huge issue that it was.
Now that the company sees the issue, it has to be dealt with quickly, sincerely and in the best way possible. They have to address the issues, or the users will run away like the flighty people they really are. If the problem is fixed well and explained within hours, things will be fine.
Of course, the only way to avoid these issues is to communicate changes before they happen, and to ensure the changes are slow, steady, and based on feedback given by the users. After all, what is a social networking site without its users?