Peter, you raise a useful point about all the crowdsourcing we see. It certainly can't replace formal market research. And there are always some ringers in the mix.
That said, the general thrust of crowdsourcing results has more than the seeds of truth, especially when there are more than a few entries. One reason for that is the free_form entries: if most of the respondents mention the same handful of issues, good or bad, then those issues are important. The issues that mentioned consistently here have to do with how decisions get made, how talent is rewarded, aging technology, attitude towards customers.
Glassdoor allows respondents to identify the part of the organization they are reviewing. Many don't but many do. You can see Irvine vs. Atlanta (I don't recall other locations), and sales vs. tech vs. marketing. I could easily imagine a longer-term channel support employee complaining about how they're treating partners; regardless, that certainly wasn't a consistent theme.
Grammar problems have always been a pet peeve for me, too. However, I've come to be a bit more discerning. Grammar problems on a resume are an automatic cut. Problems on anything submitted for consideration for customer exposure, including email responses, are no-no. But informal communication? I've loosened up; I'm more interested in what they're trying to say than whether they double-checked it. I've started seeing minor grammar offenses on postings for major news organizations; the post passes spell check, but they miss ""their"" vs. ""they're.