Hi, well I havent done any of their volunteer programmes but one of my friends leaves at the end of May to do volunteer South Africa with BUNAC - i also know one other girl who did it last year - and she said it was amazing. I have thought about doing that kinda thing too - but my experience is just with summer camp and Work America both with BUNAC, and they are ace in my opinion.
The girl who did the volunteer programme said it was a real culture shock, but her placement was really good- she lived with a local family and apparently the whole village got to know her and really appreciated what she was there doing with the other BUNAC volunteers. BUNAC seem to prepare the volunteers well as well, as everyone has to have an interview to ensure the participant is prepared for the culture shock and all - so i reckon they wud be pretty good.
I'll let u know how my other mate gets on when he gets back!