I dabbled in buying units and renting them out years ago in a complex I had previously lived in. The complex has a large number of 2-story buildings that each have 8 units. I found out that I prefer more liquid investments, and that I don't care for the headaches that come with tenants, property maintenance and repairs, paying property managers mucho $, etc. But it can be a great way to make money if you have the temperament, and if costs can be kept under control and tenants are carefully screened.
Interesting. Just yesterday I was talking with another investor and he had a very similar opinion. He said, loosely translated: "From now on all my investment will be made with the mouse of my computer. Going to court multiple times for unpaid rents, receiving phone calls from drunk tenants in the middle of the night, running left and right to repair things, calling after tenants trying to figure out if they are just late on their payment or if they don't plan on paying at all only to end up in voicemail... from now on it's just shares/bonds where I click *buy* and that's it." I have to say that I agree. I'm not completely against renting out my previous apartment if I move into a new one but even in that case, if I manage to sell at a good price, I think I'd rather sell and throw the money into more hassle free investments.