We hosted two French exchange student, and it wasn't a particularly pleasant experience either time. We provided them with a lot in terms of food (man, those girls could eat!) and entertainment and they were not at all appreciative. They didn't really contribute at all to household chores (we weren't expecting them to become a live-in maid, but unloading the dishwasher once in awhile would have been nice). They also didn't help me at all with my French. Neither stayed in contact.
The first girl unfortunately spent a lot of time hanging out with my friend's French exchange student, which would be fine except that she was not a good influence at all. They didn't like the school rules (and the lack of a special smoking room apparently?!) and I think they skipped a lot of classes, pretending they were going to art or drama with another student instead of maths with me. It didn't help that the only thing we had in common was that her parents were also divorced. To be honest, based on her experience, I don't know why anyone from France would come to Australia (or vice versa) as everything was apparently 'the same' - even the gum trees! As she and her sister had done several exchanges and school trips over the past few years I don't know if it was something she really wanted to do or just her parents wanting to get rid of the kids for the summer.
I actually knew the second girl before she came. She had stayed with a friend of mine the year before and we had all loved her, so when she said she wanted to come again I begged my mum to let her stay with us. My friend was actually from New Zealand and she and her sister were living in Australia with their aunt and uncle, who were paying their school fees. Funnily enough, about a week after the French exchange student left, there was a major blow up and the girls moved back to New Zealand two days later. I suspect that the way the aunt and uncle worshipped the exchange student may have been a factor in the fight. Everything we did was apparently inferior to the way the aunt did things - even the entrance to the market I took her through! It was probably better than the first girl, but still not great.
On the other hand, some of my friends have had great experiences with exchange students and are still in contact and visit each other years later and are even invited to weddings on the other side of the world!