In reply to Flinticus:
I kinda share your opinion. Its in some ways a holiday that let's the person feel like a hero for not really doing much. It does however educate them and make them a spokesperson for what life is like for some of the poorer people in the world and (from seeing the effects on people who've done there trips) probably makes a longterm benefit from that and the money donated or raised later.
Some are better than others. Some of these trips raids a lot more money than just the running costs and part of the job is getting much needed supplies (eg medical) out there. I ac5ually donated £40 a few months back to a lass going on one like that for 10 weeks, though that was more of a gift to her really as she's the girlfriend of my little sister, but I knew they'd both worked hard towards it.
I agree donations to MSF and similar accomplish more and have a friend who has just returned from one placement with them. The jobs they do are amazing. She got experience by doing the first kind of trip though and that helped her when applying to MSF.