I have had 6, or is it 7 years on Hobies, and been through 6 boats, many many hours of pedalling, numerous broken turbo fin masts and several broken cables but I have never had a single stripped cog...
I suspect something is going wrong: e.g. Hobie has changed its materials (knowingly or unknowingly) or people are not adjusting their drives properly?! Honestly I suspect the latter.
I strongly suspect that where these teeth are failing this will be because of 2 factors:
1. chain cable tension too loose plus
2. heavy pedalling
...with these two factors on a stainless cog drive it will be easy to get the chains to skip a cog - now extrapolate that to a plastic cog drive and if heavy pedaling can get the chain to skip despite the central locator tooth supposedly holding the chain in place I suspect the teeth will get chewed up on almost the very next stroke...
For those who think that the stainless cogs are the answer - they could be but they are no means perfect and for most people I believe that plastic cogs are possibly better: I am still using my original stainless cog drive (it is as good as new, nearly) and have recently 'down-graded' my other drive which had plastic cogs to stainless cogs but this was not anything to do with the strength of the cogs but ease of replacement of broken fin masts.
So I now have 2 stainless cog drives and for those who might consider the same modification, be aware:
1. Stainless cogs are much more prone to skipping because they do not have the central locator tooth that holds the chain - all the teeth are the same.
2. To prevent skipping I believe that cable tension needs to be tighter - this may well make the cables more prone to breakage. I did have a 'run' of cable breakages during which I had several break one after the other til I began to question the reliability of the drives but I suspect this was more to do with manufacturing defects - anyway it was purely a suspicion since I have never recorded exactly what broke and on which drives and certainly some of these breakages were on plastic cog drive(s) and I haven't had a cable breakage in a long while.
3. For people who like really torquing up their drive through hard pedaling stainless cogs are not the the way to go IMO - this is when the chains are most likely to skip and it is not too hard to get to that point unless the cables are really quite tight. While I am a reasonably strong pedaller myself and like to maintain relatively high average pedaling speeds compared with my Hobie buddy and definitely compared with normal paddling speeds, I am not the biggest or strongest guy out there...
Hope this helps.