Typically i'l use the mouse more than the keyboard in situations which don't require me to react too quickly (e.g. PvE raids, etc) to press castbar buttons, to scroll and all that. Generally because it takes less effort on my part, and like i said - i've got no reason to rush.
However, in RvR i tend to use my keyboard more for spells and stuff because its quicker, i still use the mouse for targetting though (can't afford to do an F8 fortehwin when your being gang raped by an assist train
)