I spent a week in Ecuador volunteering with a medical program...I will probably list it on my app. It was supposed to be a month-long program, but I left early due to some bad circumstances (indifferent and, I felt, misprepresented program staff, and I was robbed so I had no money). I don't feel like it was necessarily a life-changing experience, but it was interesting and I definitely learned a lot. The week I was there I spent at a maternity hospital, which was certainly eye-opening. Also, I know one of my recommenders mentioned it in her letter and it would probably look strange if I don't say anything about it in my app.
I am a little unsure as to how to describe it though. I certainly don't want to over-emphasize it, I know it was only a week, but if I'm going to list it I probably shouldn't downplay it either. Also, I am not exactly on great terms with the program staff (disagreement over money), so I am little unsure who to list as a contact person. I've heard those rarely get checked anyway though. Also, I don't really want to get into the difficulties I had with the program in my app or an interview, as that will just sound negative. Should I even mention that it was supposed to be a longer program, or just talk about the week I spent there and leave it at that? I'm leaning towards the latter option.
Based on my experience, I would strongly advise anyone planning a trip abroad with an organization to carefully research the program you are going with--don't just rely on what they tell you. After checking out the website and speaking with the program and a couple of people who had gone on trips with them before, I thought I knew what I was getting into--I didn't. Make sure you speak with people who have RECENTLY participated in the SAME program (same location, etc) that you are considering, the organization sending you should be able to supply names of people willing to discuss their experience, although if at all possible I would try to find people on your own as they are likely to be more representative and honest than people the program refers you to. These programs aren't cheap and before you put out the money, make sure it is right for you and clarify their refund policy with them (such as how money will be handled if you have to leave due to illness or emergency). Some of the organizations that send students on these types of programs are responsible and well-organized, and some aren't, make sure you know for sure which type you're getting involved with. Finally, I would say go with a friend or someone you know if you can, and try to go to a country in which you are conversant in the language--trust me, being alone and unable to communicate in a third-world country is a difficult and sometimes dangerous experience, and if you are planning to rely on the organization that sends you for support you may be disappointed.