My intuition and own experience tells me keyboard shortcut keys can be faster than using the mouse. However, some tasks like browsing the internet or a folder hierarchy truly benefit from using a mouse pointer. As is often the case, I believe there is no 'one solution', e.g. using a keyboard exclusively. I would like to argue it's important to offer both keyboard and mouse access for common operations. Depending on which input device you are holding using one or the other could be faster.
Considering the 'optimal' way to use a computer is a combination of keyboard and mouse, I'm wondering: has any research been done relating to the cost of switching between them?