I very firmly believe that the PS series can be done only once a week and produce very good results.
There is an exception to every rule, and for PS it is, in my humble opinion, that you may want to work in an extra workout for your trouble spots.
In my case, legs and triceps seem to be slowest to respond, so I will work them twice a week, but do a different workout which is not as long and intense as those in PS. I may follow the lead in the MIS tapes which is three exercises later in the week for triceps. For me, legs are another matter, and I WILL hit them with a full blown workout later in the week. BUT, if I were repeating the PS Leg workout, I would do it with lighter weights.
Isn't it funny how the same bod can shape up so well in just certain spots?! My shoulders, chest, back, biceps and abs shape up really well, but the legs and triceps need a extra little nudging.
How can I be so windy at 4:10 am on a holiday morning? ;-)