I've seen an oval that had the gate pulled out in a fall. 
  
overall you don't hear of too many accidents resulting from 
gear failure rather than human error (reading ANAM etc), but 
probably most gear failures are from carabiners  
breaking, likely in open-gate or crossloaded circumstances.  
This is my impression but I have not read stats or studies 
to confirm it. 
  
If you know the short-comings of your gear and use it  
appropriately it's all strong enough. Ovals have a number 
of disadvantages compared to more modern shapes, but they 
work fine if you take care.