I'm looking at my client site usage stats right now and I'm not even seeing any of mine get over 20GB in a month so far, haven't made it through all of them yet.
From what I read, it won鈥檛 affect 96% of sites or sites which you don鈥檛 change the plan on, which makes me feel better. I do find it worrying though, makes me realise how dependent i am on a company that can make decisions I have no say in