I've done 3 homestays for different periods of time, and I mostly enjoyed them. My homestay family in Kanazawa was the least of the 3, not because they were mean, but because they were boring. Two 60+ people living in the boondocks with odd job hours weren't really able to show me around much. Luckily I had a bus pass and good friends...plus some silly girls who worked for our program that were willing to show us the town.
My Tokyo homestay was phenomenal, mostly because I got to know them the best. 6 months is ample time to get to know people, and if you get a year, so much the better. We drank together all the time, went on numerous trips, they gave me presents, a mini birthday party, helped me with my travel reservations, helped me track down the wallet I lost in a drunken stupor, and so much more. Me and the host mom were the closest, and we used to tease each other all the time. Writing about it makes me miss them...
As far as hospitality goes, eventually they'll accept you more as a member of the family than as a guest...or so it happened with me and my friends. Politeness is forgotten and replaced with comfortable realism, like burping, drunken rambling, and gorging yourself at appropriate times. My host mom eventually resorted to doing my laundry and waking me up when i was too hung over to answer my alarm clock...just like a regular mom. They were always respectful of my space, and tried to plan events far in advance to give me due notice...though I don't think this is any different than what they do for each other.
Coming home at 11 am, spending the night at a friend's house, going on random trips...they were all ok as long as i told my host fam before it was too late (usually 5 pm, since they had to prepare dinner). I've heard horror stories, and I had a friend who left 3 months early because his host family was so bad, so it's not all candy and sunshine, but more likely than not, if they're volunteering for this, it's because they want to do it.
Have fun!
