In Northern MN, there are loads of them.
I was rifle hunting a couple seasons ago and witnessed a pack running a doe. To be honest, it was one of the most spectacularly wild things I've ever seen. I heard them first (this was broad daylight mind you- midafternoon), then a doe came racing by followed by a formation of wolves.
Of course, I was sitting in a tree stand at the time and holding my 30/.06, so I felt pretty safe. One of the "wing" wolves passed right under my stand.
I thought about taking a shot, and it's a good thing I didn't! Later that evening, a couple DNR guys came into our camp and asked if we'd seen any wolves? As it turned out, they were tracking this pack and had radio tracking equipment in their van.
I'm no expert, and I don't have supporting facts, but judging by the lack of Deer seen so far this season, I would have to say that the wolves must be having an impact. Normally, I would have seen many more does and yearlings by now. They just aren't there.
I'm not in favor of eradicating them altogether, but I don't have an issue with thinning the herd as it were.