An ideal candidate would have been bitten by bugs where the segfualt never happens because the offending code got optimized away. Once you've been bitten by that once, it become hard to answer with just "segfault".
I'm not sure it even has to get optimized away. Stuff like,
Foo *ptr = NULL;
ptr->member...
isn't going to access address 0, even w/o optimizations, despite the only pointer here being null. (It depends on the offset of "member", and if that offset is large enough, it might not be in the first page anymore. What's mapped at 0x1000 and later?)