CouchSurfing: They Leave the Light On For You

I read about CouchSurfing a few months ago in Good magazine, a new periodical which focuses on positive change. The concept is quite simple, a registry of people offering free hospitality in over 218 countries. It is set up like a social-networking site, so you can read up on someone you'd like to request a stay with, or on someone whose request you are considering. The participants love it, since it means not only a free place to stay when traveling, but a local social connection. Home-cooked meals are optional. Presumably people who sign up for this are outgoing and interested in meeting people from around the world; the CouchSurfer motto is "Changing the World One Couch at a Time". (Perhaps borrowed/ripped off from Freecycle, which "changes the world one gift at a time?")
My reaction is enthusiastic - I love building community and social capital, and CouchSurfing seems like a great example. I also am intrigued by how much waste we have in the Western world, and this is a way to redeem all of our surplus space. My brother told me, when he visited my 6-bedroom house for the first time, "Come de Revolution, 50 people are going to move in with you!" and that has stuck with me.
On the other hand, the concept of opening my house to random people from all over the world makes me incredibly uncomfortable. Some of my anxieties are
1) not being able to get rid of them, if they overstay their welcome,
2) not being able to communicate with them, since I only speak English, and
3) feeling the need to entertain them. This is not expected, it's just that I wouldn't be able to help myself. In reverse, the idea of crashing on a stranger's sofa is ... well... euww! And then of course there are the safety worries. This community no doubt has addressed all of these concerns perfectly well, it's just what comes up for me when I think about it.

The irony is that I open my home all the time to strangers, through my synagogue community. Traditional Jews don't drive on shabbat (sabbath) so must stay in walking distance of the synagogue if they are attending a life cycle event like a Bar or Bat Mitzvah. Since we just live a mile from the local synagogue, I frequently host community members' friends and family, and it has been uniformly pleasant. Since we have a guest room (empty most of the time - a waste, really), it is not especially intrusive. People are incredibly appreciative, interesting, and respectful of our boundaries. Some of them bring unbelievably nice gifts. I have often thought being a B&B hostess would be fun, though I know it's really hard work.
Pennsylvania was a destination for campaign volunteers in the [tragic] 2004 campaign, and members of local organizations were asked to house some of them. This was a little more distant that a screening process through local synagogue friends, but we figured how creepy could League of Conservation Voters volunteers be? So we did offer our home. We were assigned the head of the Natural Resources Council for the State of Maine, practically aristocracy. I felt very honored to host him. As you can see, my idea that hosting strangers would be unpleasant does not match at all with my actual experience, which has been quite positive. Is this discomfort a result of social conditioning, perhaps, in our privatistic society? Or perhaps reflective of a generation gap, since CouchSurfers are my kids' age? Fortunately there are 200,000+ active CouchSurfers, so my non-participation isn't affecting their success.
Would you CouchSurf, as host or visitor? Do you HouseSwap? Any advice or experiences to share?