My family spent two weeks in the San Cristobal program at the end of 2011. Most people who visit the Galapagos are on highly structured tours, whisked from place to place, and carefully shepherded by guides. As volunteers, we had a very different experience, seeing things that most tourists don't.
The station is located at high elevation on San Cristobal, a much cooler, cloudier, and verdant area than the hot arid coasts. They support a very wide variety of efforts, mainly centered around supporting native plant life and encouraging local people to support conservation. We spent a lot of time doing greenhouse work, sorting and planting seeds, transplanting seedlings, and moving plants around from sun to shade or vice versa. We also spent time on removing non-native plants, especially Mora (Blackberries), which has run wild.
Perhaps the most eye-opening day for me was spent at a neighboring farm 20 minutes down the road. There our task was clearing one of the farmer's fields that had become overgrown with Mora, but what struck me was seeing up close how local subsistence farmers live, raising all their own food (pigs and chickens running around the yard, and a few cows for milk), and living in a house they constructed themselves of local materials. For years I'd heard the Galapagos described as pristine and mostly untouched, but it's important to learn that people have lived there for a long time, still live there now, and are an important part of the story.
Other work we did included tasks in support of the station, such as collecting fruit from the surrounding forest, helping prepare meals, and even hauling lumber out of the forest for construction. (When they need wood, they cut down a non-native tree and turn it into boards by hand.)
The work is 5 days/week, with weekends off, so most people head into town on the weekends to enjoy the beaches, snorkeling/diving, restaurants, and tours. The station is also flexible if you want more time off, for doing a multi-day island tour, for example.
The station can accommodate up to 50 volunteers, though we were there at a very quiet time with around 15, though every few days people would arrive or depart. Most of the volunteers are in their 20s; as a family we comprised both the youngest and oldest people there. Our youngest, then 9 years old, could not officially be a volunteer (we had to assume responsibility for her), but they were quite good about finding tasks where she could contribute as well.
On the whole this was a great experience. We were able to see a very different side of the Galapagos from what most tourists see, and also contribute toward improving the islands for everyone.