The power of social has turned the way business does business upside down and that includes their “employer brand.” So it is a double standard if you will that open/transparency applies to both companies and people. It’s forced companies to quickly learn social network etiquette.
However, just because it’s on the net in a forum doesn’t necessarily make it credible. It’s the quality of the individuals(more often friends or associates you trust) delivering the insight that does. Sites like Jobvent.com or Glassdoor.com are interesting to get a bird’s eye. But keep in mind some of those comments are disgruntled past employees, and competitors. You remember that heavily popular site called F’d company.com which is no longer around.
This is an article from Business Pundit that talks about those sites. Drea asks at the end of the article if you had ever researched these sites before interviewing with a company. More people are starting to do so again.