This is an amazing trip. Please do not underestimate the physical challenge, but the trek is worth every step at the end when Machu Picchu awaits. All the porters, guide, etc. are great, if you like the outdoors and want to experience first hand a little bit of the "Inca" this trip is for you.
Don't expect 5 star hotels and flat trail. You will meet great people in your group and maybe friends for life. This is the only way to see Machu Picchu without cheating. Do the Inca Trail and you won't regret it. Steel city (Sheffield) mountain man !