I currently do this. The only reason it works for me...
1. we were friends before hand. i knew his party habits, his line of work (bartender and in school)
2. we both arent perfectly clean, we get in tiffs occasionally, but we work it out, because we are friends. i have a doberman which adds to the mess, and hes working on not leaving stuff laying everywhere.
3. hes a non-smoker, single college guy, no pets, and also into staying in shape, and similiar hobbies. I wouldnt date, nor will i rent to a smoker. He has also been respectful so far about bringing back women, which is very nice.
4. for a while there i needed that extra income per month, now it just helps me live a more comfortable lifestyle. ive looked at it different ways ( pays half the PITI, or pays my harley and insurance :) )
Renting a room in an older house is a challenge, or any house where you share common spaces. If you have a multi-level home where they can have the basement and only share the kitchen at worst, then it works even better.
I intend to move up to the attic in the future, which will help. If my girlfriend ends up living with me, we will ahve to figure that out, they get along, but if she moves in, I imagine it will no longer make sense to have him for the extra income, unless i finish the attic/basement, to add more space.