Never felt threatened in Manchester, even when alone or walking about late at night. There again, I don't have any need to venture into the worst areas. As for things like burglary, I know plenty of people who've had their houses/cars broken into. My car was broken into during first year. In second year, my Dad was preparing our student house (he's our landlord) and somebody broke in via a window before he managed to scare them away. We live in one of the 'safer' areas, directly opposite the MP's house and right next to the Chinese Embassy. So, things like burglary I'd say are pretty common (most people I know have been subject to burglary/attempted burglary) but the whole "you're going to get mugged, then raped, then shot" thing is a little overstated.
Wouldn't let any of that put you off though - just don't park anywhere dodgy and ensure you've got decent house security (ours is now upgraded since attempted burglary). Oh, and take out decent contents insurance for your room/house!