I had a great time on the Salkantay Trek. Although I have to say, the second day really is tough. Of course, you can rent a horse if you want. Some of their info is a bit outdated, though. For instance, I brought water purification drops which turned out to be unnecessary since there are a lot of little shacks along the wast which sell water and snacks and such.
The views were great. It's really a beautiful trail. I've heard that the Lares trail is also very nice, but with a lot less people. I hope that this company, as well as the others which organize this treks do something about cleaning up the trails and the campgrounds, as far too many people evidently have no problem throwing paper, plastic bottles, orange peels and the like on the ground.