I know two people who wear them at OCIN events, but I prefer big cleats to the skinny spikes. On a track, I see people with short spikes, maybe 1/4 inch or so (?). For cinder tracks (or trail?), you can put in 1/2 inch (or so) spikes.
Whether it's a good idea to use track spikes on trails or in the woods is beyond my experience. I think of track spikes as extra-lightweight uppers that last one track season if you're lucky, but we always bought the cheap ones intended for team purchases.
Full-disclosure: I don't own a pair of O'Shoes right now. The last pair I had was in 1988 or so, and they were the Adidas Orienteering model. I wore them until the uppers fell apart. I've been putting off buying a pair of the metal-studded ones, but this summer I'm probably going to. Right now I go to the sporting goods stores and look for the cheaper cleats for soccer, football, and baseball. I pick something with heel padding (important!) and big cleats that look like they'd shed mud. Here in Cincinnati, my experience says: If it's dry, anything with tread works, even running shoes. But if it's wet and hilly, you want the biggest cleats you can find.
I hear people talk about the width of the heel area, and how they don't want a wedge at the heel, because it twists your ankles when you cross slopes.
I like a lot of grip in the heel for braking on downhills. Also, soccer cleats often don't have a hill-climbing cleat at the toe, because they don't want the toe to catch when kicking.
In the UK, I've noticed they call it "Fell Running", and they have a better selection of shoes than I've seen in the US. Example:
CompassPoint O'Shoes/Fell Shoes
I am not an expert in this area, so don't give a lot of weight to my contrarian opinions...