Disable Mage_Log module observers

config.xml

<config>
  <frontend>
    <controller_action_predispatch>
        <observers>
            <log>
                <type>disabled</type>
            </log>
        </observers>
    </controller_action_predispatch>
    <controller_action_postdispatch>
        <observers>
            <log>
                <type>disabled</type>
            </log>
        </observers>
    </controller_action_postdispatch>
    <customer_login>
        <observers>
            <log>
                <type>disabled</type>
            </log>
        </observers>
    </customer_login>
    <customer_logout>
        <observers>
            <log>
                <type>disabled</type>
            </log>
        </observers>
    </customer_logout>
    <sales_quote_save_after>
        <observers>
            <log>
                <type>disabled</type>
            </log>
        </observers>
    </sales_quote_save_after>
    <checkout_quote_destroy>
        <observers>
            <log>
                <type>disabled</type>
            </log>
        </observers>
    </checkout_quote_destroy>
  </frontend>
</config>

<events> tag is missed:

<config>
<frontend>
<events>
...
</events>
</frontend>
</config>