There are two kinds of Philofaxers in the world...those who find an accompanying hole punch indispensable and those who will never own one.
I'm of the first camp. I have 6-hole punches for both my Personal and A5 Filofaxes. I like to punch "outside" pieces of paper (sometimes with trimming) to carry with me...schedules, maps, information sheets, and so on. I always buy A5 journals with perforated pages so I can use the same paper in my Filo. One time I punched a postcard of a museum display I wanted to see!
If you print your own forms, like the ones Steve makes and offers for download in his Yahoo group, a punch is a must. (Although sometimes I print information from Word documents onto the blank leaves Filofax sells, which are of course already punched.)
The one problem I'm having: I haven't figured out how to empty the paper chads out of my A5 metal punch. Does this plastic cover just pull off somehow? I've never been able to do it.