We designed the Cloud hosting to be infinitely scalable. As a result, we decided it was never in customer interest for us to take a site down, especially if it was so busy as to exceed bandwidth.
We therefore have a fairly relaxed policy towards bandwidth exceeders as we necessarily have lots of spare capacity. If you exceed your bandwidth we will get in touch and tell you to upgrade for the next month. If you are on one of our smaller packages we will suggest you upgrade to the next package up.
Just to clarify, on our Cloud hosting packages we will not suspend your site for excess bandwidth. This is different to cPanel where if your site exceeeds a bandwidth limit it will show an error.