My trip on the Inca Trail was a once in a lifetime experience! I suggest that if you even think you may want to do this, you do it! Nothing makes you appreciate Machu Picchu itself more than finally seeing it after 4 long days of trekking towards it.
Carlos (our tour guide) was fantastic! I recommended him to my cousin going in December - he is personable, funny, and the way he calls you 'my friends' is simply amazing. He has fascinating factoids, funny stories, and tales that will leave you wanting more. If I had to do it all over again I would go with him for sure.
You feel comfortable and welcome not like you are on a giant tour bus with a bunch of strangers. Oh! and the food was pretty great (way better than I had expected). Also I worried that because I was not in great shape or having enough time to 'acclimate' I would have trouble, but I didn't and when I did go pretty slow Carlos was there to motivate me and never left me behind! What a great trip.