Buying a Multi-Unit House

I think I am going to go look at a duplex or two. I love the idea of living upstairs and renting out the bottom half because I can stilll spend money like a dope if someone else is paying most of my mortgage. My concern is the amount of necessary maintenance. I live in a duplex at the moment and over the year and a half that I have lived there we have only had one minor mechanical problem so, I wonder if it is a decent gamble. I'm sure the condition of the house is a big factor but I am curious if there is anything else I should be looking for. Has anyone ever owned a multi-family property and rented a unit? Any advice?