I have friends from Södertälje, who say the town's become a no-go area for police since the riots a few years ago, when the police station was attacked after a couple of Syrians were arrested, and is now controlled by eastern European, Russian and middle eastern gangs. It doesn't bother them though; they're all friends with the immigrants and wouldn't be touched, but a Swedish girl was attacked a while ago for walking through a muslim area without wearing a hajib, and they say there's a great deal of organised crime in the town now. Also, one of their friends got tasered by some Turks on motorcycles, out for a laugh, but they accepted that as normal.
The immigrant situation is much different here in Glasgow; all the immigrants here tend to be productive citizens with jobs, and the younger ones go to uni and stuff. Unlike Sweden, they haven't recently come from warzones and the like, so they're far better adjusted. It's the mostly native neds here that cause the problem, but they don't have the intelligence or organisation to be really dangerous. That said, Glasgow gets about 50 murders a year, and is the stabbing capital of Europe, or so I've heard, but I'm not an expert on Glaswegian criminality.
Anyway, seems that the problem isn't so much that there's immigrants, but that the immigrants going to Scandanavia come from some of the most deprived and traumatised places in the world. Our post WW2 wave of immigration was completely different, and was composed mainly of workers with families coming over from India and Pakistan to fill a gap in the job market, rather than fleeing some disaster and ending up on benefits.