[jonnathanson]

The conflict of interest (companies are also advertisers) is powerful, and it appears to be exerting a significant effect on the directional reliability of aggregate reviews for any company large enough to be a major advertiser. Companies can badger Glassdoor into removing negative reviews, and Glassdoor will ask few to no questions before taking summary and unappealable action in the company's favor.

The negative reviews are pretty much the only interesting data points on the site. Take them with a grain of salt, sure. But you have to take the positives (especially large cohorts of positives over short time intervals) with the whole freaking salt shaker. The aggregate scores offer some directional guidance, but bear in mind that you are not looking at the total sample size of reviews; you are looking at the sample size after the company has culled and gamed what it can, which is often quite a lot of the original pool.

This is sort of like the directional reliability of eBay scores, now that there is a short decay on past reviews, and pretty much anyone with 10 minutes on their hands can get negative reviews expunged.