When I lived with parents we all had to share a family PC, drove me mad as my bro was a keen gamer aswell and my little sis liked to surf. Whenever somthing went wrong with the machine it was always my fault. So I got my own and have never had any problems with it ever!
They continued to have loads of issues with their one but every so often I'd set it right. Now I've left home it's finally given up, shorting out the motherboard, CPU and all the drives, gawd knows what they did to it but I know it never got a clean since I did it last,,,, ages ago....
Now I live with my girlfriend, we both have a computer each, well actually I've got my Computer and a work Laptop and she's got her own PC (which I built), a laptop and some brick of a shuttle. Since having her own PC for 1 year she's managed to mess it up big time with the only cure being a clean install of windows....
No-one uses my PC ever, I just don't think I could trust it to anyone.