This is more of a housemate, rather than roommate situation, but it was still kind of hellish...
The first year after I graduated from college, I lived with a roommate, and things weren't fantastic, but they weren't terrible either. After that lease ended, I was looking at different options, and saw an ad for a housemate. Rent was $500 per month, which included electricity, Internet, water, cable, and use of the garage. I met with the guy who owned the house, Kofi, and he explained that he traveled all the time for work, and so was looking for a housemate to offset some of the bills and give the house a more lived in feel. I moved in, and all seemed well for a couple of weeks. There were two other women living there that he'd never mentioned, so that was a little odd. He never gave me access to the garage, which was annoying, but not terribly so. I just parked on the street in front of the house. He seemed kind of unhappy when I asked for his network password, but gave it to me. Then he started giving me the hairy eyeball when I set foot outside my room, no matter what I was doing - making dinner, watching TV, etc. He'd give me weird looks and ask what I was doing, why I needed to be there or just sit and watch me. It was creepy and weird, and made me feel like I was in the wrong for being in public areas of the house!
After about two months of my living there, he told me that he'd noticed his electricity and water bills were really going up (yes, this is what happens when you go from one person living in the house for about a week out of every month to having three people living there full time!) and so he was going to have to start charging us for everything that was initially included in the rent. Based on the numbers he gave me, I was going to end up paying $650 a month for a room! I did some research and found out that studios were available for about $550 a month. I gave him a full month's notice. He freaked out on me, and tried to forbid me to use any of the common areas, since I was "betraying" him by moving out so soon after I'd moved in. I have never been so grateful to move out of a situation!
Living by myself in that studio was a bit of a financial squeeze, but totally worth it!