I've been living close to Derby for about seven years and often come into town on a Friday night. Never had nor seen any trouble of note. There are a number of decent bars around Irongate, Friargate, etc. in the centre of town. Monday nights are generally quiet, like most places.
One of the best gigs I ever did was in Derby. At the warehouse I think. It was with Ash just as they broke. We had 400 kids in a 120 capacity venue and it was punk as f***.