Ribbons are good for applications like Word, where you are constantly interacting with buttons and toolbars, and need them available. In IE, you use maybe 2-3 buttons tops, and all the rest are rarely used (Print, Options, etc), so it makes sense to hide them. Personally, I think additional toolbars in browsers should be discouraged, not encouraged: they are almost universally bloated and useless, replicating built-in functionality and adding dozens of buttons for no reason.