For instance: looking at a recent review of my company from a few days ago, it saddens me to read something written so well that is so inaccurate. The content opines that people of color would not be welcome at our organization. I cannot tell you how completely FAR off that is from the truth. Diversity is something we value tremendously. That being said, we are a tech company in the agricultural space that is located in the midwest. The fact of the matter is: our pool of candidates is simply not that diverse to begin with.
Because we are a small startup focusing on survival, we hire the right person for the job, regardless of their background! Ethnicity, sexual orientation, gender, etc... is never part of the decision! When this sentiment was shared with the organization, the reviewer interpreted it as "we do not care about diversity and people of color". Not making a specific point to hire diverse folks is NOT the same as not appreciating a diverse team!
Now this is almost a self fulfilling prophecy: a person of color might read that post and be completely turned off from even giving our company a shot. It hurts to imagine this scenario.
Long story short: the unhappy folks are usually the loudest and so I think you'll tend to get the 'jade colored' glasses.
Another anecdote: my fiancee was warned by a friend who previously worked at a company she was interviewing at. This person warned her that her manager was mean and grumpy and she'd be unhappy there. My fiancee has been there for months now without any problems whatsoever, and this manager tends to confide in her more than others on the team.
So I think you need to use every available resource you can to gather data points that can feed into your decision... but a lot of it needs to be taken with a grain of salt.