As a current finalist at Notts, I would say that the crime rate is something to be aware of, but not necessarily something that should put you off the university. In your first year, the likelihood is that you will be living on campus, in which case campus security is relatively good; although obviously you need to watch out for things like leaving bikes unattended by the entrance or your laptop in an unlocked hall bedroom.
Equally, during their later years at Nottingham, while many students (including myself!) do choose to live in Lenton/Radford/NG7, the aforementioned second worst crime district in britain, it is also possible to live in one of the safer student areas like Beeston or Dunkirk, which are less prone to crime but equally, less good for pubs and general student hijinks.
Even if you do live in one of the dodgier parts of Nottingham, there is generally a massive police presence, with a Neighbourhood Warden scheme (I was once offered an escort home by the police when I tried to walk back from a Lenton pub by myself!), and there are lots of things students themselves can do to protect themselves from crime. The SU takes a lot of trouble to make students aware of safety when living out.
As for gun crime, this is something that is much talked about in the media, and while it is a genuine problem in Nottingham it is not something that really needs to worry a Nottingham student -- it is after all targeted, organised crime.
My house was broken into in second year and I would advise any students moving into Lenton to really -listen- to all those warnings about not leaving windows open and not all very obviously leaving the house together on a Thursday night. But despite that unpleasant experience I am still incredibly glad I chose Nottingham -- the bad has definately been outweighed by the good.