Inti Raymi used to be a sacred ceremony for the Incans, but tourists and the Peruvian government are making it more of a tourist attraction. During the 2008 celebration the Peruvian Government forced Peruvians and tourists alike to pay $90 dollars to be seated where they could see and hear the performance on Saqsaywoman. Many Cusquenas and Peruvians cannot afford to pay $90 for a seat. To put that cost in perspective, a taxi ride in Cusco costs 67 cents, a stocking hat costs $1, and a croissant costs 7 cents. Feeding their children and themselves comes first for the Peruvians.
The ceremony begins in the Plaza de Armas of Cusco where performers dance in bright colored costumes and act the traditional Inti Raymi script. Donations of Corn (Maize) and Coca leaves (FYI: Coca leaves are the main ingrediant in the drug cocaine, but locals use it in tea. The tea is considered a cure-all from everything from a stomach ache to altitude sickness) are given to the Sun God, Inti. The performance is moved to the Incan Ruins on a mountain above Cusco. The locals walk to the top of the mountain from the Plaza de Armas while the tourists were given a bus ride to the performance. The tourists were easy to spot because many tour groups had bright colored hats so their tour guide wouldn't lose them amongst the thousands of people.
The locals were seated on a surrounding hill watching the performance. Vendors sold potatoes, sunscreen, handouts, guinea pigs (to eat), sunscreen and many other items. A hill closer to the performance was blocked off for "safety reasons", but during the performance the people broke through the police barrier and stormed the hill. Thousands of people stormed the hill, shouting and cheering. From here the view was much better and the performance could be heard also. The people waved the flag of Cusco and Peru with great pride.
After the performance the Peruvians slid down the ruins.
I lived in Cusco for 3 months in a service-learning trip and attended the celebration in 2008. All information came from observation or talking to locals.