I telecommute as well and basically have the first six hours of everyday by myself, so I feel very productive during that time. After lunch it drops some, but luckily that is also when meetings are so I feel it doesn't matter as much. If I still have time left and don't feel very productive (which happens maybe one day a week, sometimes more though) I usually have some work that doesn't require much mental effort (like administrative or light maintenance) and work on that. If I couldn't define my schedule like this it would probably be harder.