I have an 18t Surly cog that I used through 1 winter (maybe 5 months) and the teeth bent all to hell. They look like little waves curled to one side. I've had a DuraAce 16t for maybe 8 or 9 months and it's only bearly worn. The 14t Shimano that came with my bike that shows less wear, though I have the feeling that only ever saw the track before I got it. The body of the cog and the teeth is roughly twice that of the Surly.

And no, I've never stripped a cog off of either of the Surly hubs that I've had. I had a year on the first one before it was stolen, and a little over that on the new one. One thing I reccomend with the hubs is to replace the wide locknuts on the cones - if you tighten the tracknuts down too tight, you can crack and destroy them. Put new nuts on before you ride it too much.