The Due North All Purpose Traction Aid (http://www.surefoot.net/) is great slip on traction device that works really well when you need something to give you some traction in a bit in less gnarly conditions. This morning I had my first opportunity to try them out. We got about 3" of snow overnight- not much, but enough to make the roads and trails slippery. I headed out for one of my usual routes, which is about 10km, with 4km of road and 6km of trail. The snowplows had just gone by, so the side of the roads were packed snow, which is very slippery when wearing road shoes, not too bad when wearing trail shoes, and no problem when wearing these. I felt very solid, with no slipping at all. The spikes on these (picture below) are small enough too that you don't feel them pushing up into the bottom of your foot when you're running on a harder packed surface, so it doesn't feel like you have anything other than your shoes on your feet.
When I got up to the trail I could feel that these were giving me a bit more traction than if I hadn't been wearing them, but still was slipping a bit as the spikes just aren't quite long enough to dig in to deeper and sloppier snow. I also lost one of the spikes, I think happened when I stepped on to a log buried under the snow and kind of slid along it a bit. They come with extra spikes, so I can just pop one of the replacements in.
In summary, these are perfect for runners who normally stay on the roads and sidewalks, but need some traction for when it's snowy or icy. They're lightweight, comfortable, and give you a real sense of stability where you might otherwise be sliding all over the place.