The 20 cases for underflow and overflow [0] show how difficult it is to develop error-free contracts. Would have been great if the VM would detect such cases and thus make the contract code less polluted with boundary and overflow checks.

Some projects have started sharing audit results publicly directly in their repos [1]. It's a great read to see common errors and yet unsolved issues that originate in the ERC20 token specification.

[0] https://github.com/ConsenSys/smart-contract-best-practices#i...

[1] https://github.com/status-im/status-network-token#reviewers-...