I can do better than that Nick... The incident you mention above was on the maiden voyage of my Shrike-R when Paul M. managed to crack my deck with his elbow whilst we were getting him back into his boat after a swim. That was down to the excessive amount I'd bent my plywood deck around my goalpost shaped masik, which had clearly resulted in too much stress in the wood, which was looking for any excuse to split. Since then, I helped Paul build his own low-volume Shrike using 3 separate panels, rather than one panel bent round beyond its breaking point. The result looks brilliant - I think it's the best looking Shrike deck I've seen, and it allows us lanky buggers to fit our knees comfortably into an extremely low volume boat.
I've also had my hull holed when someone who shall remain nameless inexplicably rushed in to 'rescue' me after I failed an 'exotic' roll I'd been learning. When I rolled back up using a basic roll, I found their sharp, pointy end was embedded in the side of my boat.
Finally, I once found myself unintentionally running 1" deep white water in my Shrike-R which resulted in the sharp rocks knocking a hole in the hull under my backside.
Bringing it back to Simon's question: yes, I've proven you can hole these boats, but it takes some pretty careless paddling, and it's a doddle to fix them after. If I make another one, I'll definitely stick with 3mm ply without any glass cloth as that's proven more than adequate for normal paddling and general knocks and wear and tear. For the three incidents mentioned above, there have been hundreds more which have resulted in no more than minor scratches.