In general - you will only get PIN problems if you have set some sort of 'parental control' on you Digibox.
The only time a box with no parental control should ask for a PIN is an early evening 18 rated film.
But if you set almost any sort of parental control - the PIN is then common.
It is best to leave the parental control to TiVo on a TiVo controlled set-top-box.
On my TiVo controlled Digibox, I have not yet had one PIN problem - and it is quite busy overnight.