if ((stage == CrowdsaleStage.PreICO) && (token.totalSupply() + tokensThatWillBeMintedAfterPurchase > totalTokensForSaleDuringPreICO)) { msg.sender.transfer(msg.value); // Refund them EthRefunded("PreICO Limit Hit"); return; } It is better to user revert here?

ERC20 explicitly says: Note Transfers of 0 values MUST be treated as normal transfers and fire the Transfer event. Yet, your code return false on 0 and do not call Transfer event. if (balances[_from] >= _value && allowed[_from][msg.sender] >= _value && _value > 0) { I guess, it is not fully ERC20 compatible then.

Amazing article. It might be a good idea to specify visibility modifier for functions explicitly.