I grew up and lived in Manchester until high school, when I moved to West Yorkshire with my parents, but most of my family are Manchester based and Manchester born, so I was there a lot after that. I've always thought the hatred was a little one sided. Especially growing up there in the early 90s, the hatred from United fans seemed to be focused on Liverpool and Leeds United, even at my school, where reds and blues seemed to be a 60/40 split in Uniteds favour. When I moved to Yorkshire and went to a school where Leeds United fans were the majority, there was definitely a shift in hatred. To me it seemed like Leeds fans hated us more than City fans did at that time, and that was probably reciprocated. Leeds were closer to being a threat on the pitch as well.
Now I live 300+ miles north, so I don't know what the tension is like between the two sets of supporters, and I don't know if it has shifted since City's takeover and recent successes. I'd still predict United fans have more animosity towards Liverpool though. A lot of fans here wanted City to win the title, when it looked like Liverpool had all but sealed it. I can't see that situation ever being reversed.