I worked for an exchange and it was not blocked there. I worked for a car automation company and it wasn't blocked there either. My following two jobs were at multinational banks. In the first one, it was blocked. In the second, I took a "social media responsibility" training and I was added to the exclusion list and I could access Facebook, Reddit, Twitter etc. Now I work for a small finance company and the network is wide open.
No it is not but I remember a hospital in Central London which Facebook was blocked in. I'm not sure if it was a policy or they had an issue with their network!