There are obviously some bad seeds in the bunch, and even more that house foreign students as a business, but by all means do it! I had a situation where my señora definetly used it as a business, and there were some little changes that I had to make to my lifestyle to get by properly in their house, but isn't that one of the reasons we go to Spain in the first place? To experience a life different from our own. The lessons you learn about spanish culture, food, history, and the always present language, are really unobtainable in a different situation. And if all else fails, if you don't get along in thier house, you can always move out and find a place with some spaniards, I eventually did that, and it worked out great. I even could return to my señoras house for luch whenever I wanted to!
I say by all means do it!

LCQ

Michael, there is definitely a correlation there. Salamanca has not only high international population, but high population of Spanish students. Many of them are from surrounding cities/regions and therefore pay to stay with families as well. There were no dorms in Salamanca. Therefore, it is definitely a means of income for a lot of people who would otherwise not be keen on inviting strangers into their home - especially in a depressed economy. I found it very hard to tell my "family" up front that I was leaving, but that is because I am a wuss. Legally/financially there was no problem, because I left before the second semester started and therefore there were no disputes over money. I don't know how that would work for you, but I am sure that if you are really unhappy with your family, your program will make every effort to find you better housing.

I think the issue of foreigner/student overflow and its effect is probably different in Valencia. They would undoubtedly love any gifts with regional flavor that you might bring with you. That will be a nice way to get off on the right foot.

I know there is at least one residencia in salamanca near the catedral. I'm sure there are at least a couple of others, I don't know how many though. The family I stayed with in Salamanca had many gifts from internatinoal students throughout the years. They had mentioned that they constantly have international students staying with them, whether they were other europeans, spaniards, or americans. They were still really great people though! Not in anyway strict with us. The only thing, which is completely reasonable and normal is that we couldn't make calls from their phone. I'm just hoping that I'm as lucky this semester in sevilla as I was over the summer in salamanca.