Used almost 40Gb yesterday watching 9 hrs tv. Doesnt this seem excessive?
Depends what you're streaming. Netflix, for instance, lists their streaming rates as:
Do you return your Roku to its Home page when done watching to prevent it from continuing to stream in the background?
There is also a Roku "bandwidth saver" option which stops streaming activity if there has been no user input for four hours. Settings > Network > Bandwidth saver