First, the technical documentation says things like: "Transaction fees are voluntary on the part of the person making the bitcoin transaction, as the person attempting to make a transaction can include any fee or none at all in the transaction." It is highly misleading to say that this is true because the user can modify the client.
Second, the client has an option to set the transaction fee per KB to zero. This creates the user expectation that they'll never pay a transaction fee. It is not made clear that this is not the only source of transaction fees.
Third, there is no way to see ahead of time what the transaction fee is going to be. This creates problems in cases where the user is trying to ensure the recipient gets a particular number of bitcoins.
Nothing is false or incorrect, just highly misleading.
That.
And I did not knew about the second part. (I thought transactions fees are always set per KB, they aren't?)