Cowboy is exactly correct.
In my experience, Tanzania is a very civilized place. I've lived in TZ for 8 years now, have been in East Africa for the last 15. I think it's a great place with good people.
I haven't lived in Dar es Salaam, but have spent a lot of time there over the years. I'm sure it has it's places, but overall I've found it very safe. When I think of Dar compared to other cities- Nairobi or Kampala, Dar seems very tame indeed!
I'm more nervous walking around European or US cities.