In all of my travels to Peru, I have not done the MP thing. I have always been there for work and have never spent the time on the back end of a trip to do MP. However, I have been in and out of Cuzco numerous times on my way to other places. I would sugest that anyone making the trip from North America-LIM-CUZ spend the day of arrivial resting and adjusting to altitiude in Cuzco. You are going to be drained from the trip as it is. Spend your first day laying around and resting.

Regarding altitude sickness, anyone can get it even if you have never had it before. I have known people to get it who have worked at altitude for years - even Peruvians. The only real cure for it is to get to a lower altitude FAST. If you have a true case of altitude sickness, it won't pass with time and will probably only get worse if you stay at altitude. Altitude sickness can be fatal. Treat it with the seriousness it deserves.