Jassper:
Doesn't that cause a bit more current consumption by the processor? If it's pulled to a 5v level via internal resistors, power must be flowing.
I have a handheld gadget that: runs from 2 AA alkaline batters, is used a few times every day, for 30 minutes to one hour. This is the third year of its existence and it is still running problem-free on the original AA batteries. The unused pins are held high by internal pullups.
In my experience, any current consumption from the internal pullups enabled on unconnected pins is so very small as to be essentially zero.