My wife and I had a short chat this morning, it appears that the housing glut in our area and the adjustable mortgages is causing more people to go the route we've been going for over a year, which is renting out rooms. This came to be a realization when last night one of our roommates wanted to give us a heads up that he may be moving out next month. One of his coworkers offered him a room to stay at for $200/month (I'm assuming utilities included, because that is our arrangement at $350/month for him). Math wise, the person must be desperate for money, if you consider utility costs alone for a person come out to about $60 (water, electric, heat, internet) in a shared housing environment (based on our experience). We are going to offer him $300/month and see if he is willing to stay, he was going to check out the place first before accepting the $200/month.
Another item we have noticed recently is several people from our church have independently asked about how we manage it, how much we charge, how we find renters, etc. They probably are going to be doing the same as us, but probably not at our scale of 4 rooms. I did a search this morning on Craigslist for under $300 in the Chicagoland area and I found a lot more than I have found before. Now some of those probably don't include utilities, but I found some that did.
We also decided to make our base rent be $300/month. The new roommate coming in after his first month, we'll bring him down to $300/month (he has the smallest bedroom). The couple moving in at $400/month, we'll bring them down to $350/month (largest bedroom). Our roommate that has been here for a year we will keep her at the $300/month. My goal for the coming year is that we average about $1K/month, which means we won't be able to have a vacancy every month.