I did the Salkantay Trail, 5 days, 4 nights and I have to say that it was a wonderful experience. Together with 6 other people we had a great time.
Our guide Yang is a very nice, funny and knowledgable guide who guided us in a fantastic manner through the 5 days. We also had two cooks and two horsemen who did a wonderful job. I am still asking myself how the cooks could create three times a day so wonderful meals.
The nature is great, be prepared to less oxygen, take some pills With you, just in case. An ice old see at 4200m, two of us tried :-). The warm thermal fountains everyone tried. The Salkantay Pass at 4630m has a great view to the Salkantay which is 6200m. The Zipline Adventure was opctional but worth every extra Euro. Nothing to say about Machu Picchu itself any more, simply majestic.