Not much actually. The apartment upstairs pays for right around 3/5s of the mortgage. The entire property was UNDER 175K. Its in a historic neighborhood...which is usually very nice. It is NOT an upper class area but nothing remotely close to being the projects...right in between with a mix of pretty cool folks.
Multi-units are the way to go if you are looking to own a first home. Of course you also have to play landlord. Which can be easy or down right painful at times. Not for everyone, but makes life easier when it comes to paying the "rent".