I take what I read on Glassdoor with a grain of salt. Most people bother to say anything about their companies but since they also are an employment website, I think they must do some degree of filtering the reviews. Playing both sides. In many cases, it's mostly the "sour grapes" people who post the negative reviews, and the positive ones are posted by HR. Just look at Garmin for a great example. Just snicker too about how Garmin ads say about how much they laugh at work. Ha! When I interviewed there, everyone was looking down & looked like deer in the headlights.
In addition, I hate the way Glassdoor seems to gather intelligence on anything I do. For example, they send me un-solicited emails when I just happen to look at job opportunities. Just creepy.
I wouldn't be surprised if they will show up in banner ads sometime.