We joined the Inca Trail part way through due to our arrival via the sublime Salkantay Trail (essentially starting on Inca Trail day 2). I don't think we missed much by skipping the first day and it was a bit of a culture shock joining so many other tourist hikers compared to the last four days where we had been truly 'off the beaten track'.
The Inca Trail is well maintained, well organised and very popular with a wide range of international travellers. You'll see all sorts attempting the trek ranging from bionic men to couch potatoes ... the latter are just doing more wheezing and complaining ... but 99% reach Machu Picchu.
Whilst we have fond memories of the Inca trail, it is a trek that looks more adventurous in holiday brochures than it actually is. There's something about walking a man-made stone path, cluttered with walking-stick-toting tourists (half of them speaking in an accent not 50 miles from where you live at home), that takes the adventurous edge off it.
If you're thinking about Machu Picchu then hiking to it via the Inca Trail (or another) is without doubt the best way to travel. Arriving by train / bus must be such an anticlimax for those who have flown thousands of miles to see this lost city. If you can tag the Salkantay Trail on the front then it will be the trip of a lifetime.