On one system that I have this plugin set up on, I'm seeing debug messages for some forms.
Looking over the code, it appears that GFSalesforceWebToLead::push is looks like fieldtemp is not always an array when it hits the foreach block.
E.g. foreach( $fieldtemp as $inputKey => $input ) ...
I'm expecting that $_POST["input_" . $field["id"]]; does not have an array as a value in all cases. ( e.g. perhaps the code should reference $field["input_" . $field["id"]] instead? )
Anywise, just a heads up as this might be causing other issues.