Pros
My view is that it's a good company, a growing company dedicated to emerging technology and open software, and a company that works hard but tries to have fun while doing it. Did I mention it's growing? When I started - not quite 3 years ago - there were 250 employees; now there are over 800. It's a casual work environment, but the workload can be intense. That said, I don't think I've ever worked over 55 hours in a week - and that's being in an on-call rotation. Management takes work-life balance very seriously.
Cons
I'm not surprised to hear the negative reviews of former employees. Some of them seem to be sour grapes, while others mention common ailments of companies everywhere - trouble getting promoted, the presence of cliques and "favorite sons," a middle-sized company still holding on to a startup company mindset - all true to some degree, but perhaps exaggerated by ex-employees with a grudge.