I have volunteered with Global Volunteers on the Blackfeet Reservation two summers in a row now. The people there are welcoming and warm and many have become like family to me. The program itself has been around for a long time, and all of our partners on the reservation are happy to see the volunteers come every year.
Driving around in the big Global Volunteers Van you begin to feel a bit like a celebrity because people are always asking you if you are one of the "Globals" and telling you about a new work project that the team can do. There is no shortage of work on the Reservation, but there is definitely a related culture shock for many volunteers.
As other reviewers have mentioned, the pace of life there is very different, especially if you are someone who is punctual, and rigid about order and control. Work projects may fluctuate day to day, based on this pace and the availability of materials and local people. You may find yourself doing a few different work projects but that affords the ability to meet more people, and create more relationships which is really the whole goal. The work projects are there, not only to get things done, but to facilitate cross-cultural understanding and create relationships with people.
I highly recommend this program for just about anyone. The people are amazing, the scenery can't be beat, and the flexibility of the work projects assures that your skills will be put to use. Oh, and did I mention Indian Tacos?! Delish! (PS- Indian is not a derogatory term on this particular reservation and they are indeed called Indian Tacos).