Logs file uploads for single file and multi-file upload fields pre and post submission to the Gravity Forms logging add-on: http://www.gravityhelp.com/downloads/#Gravity_Forms_Logging_Tool

log_uploads

add_action( 'gform_pre_submission_8', 'uploads_log_pre_submission' );
function uploads_log_pre_submission( $form ) {
    foreach ( $form["fields"] as &$field ) {
        if ( $field["type"] == "fileupload" ) {

            $id = "input_".$field["id"];

            if ( $field["multipleFiles"] ) {
                if ( empty( $_POST["gform_uploaded_files"] )  )
                    continue;

                $uploaded_files = json_decode( stripslashes( $_POST["gform_uploaded_files"] ), true );
                GFCommon::log_debug( "Field: {$field["id"]} (multipleFiles) \$_POST - " . print_r( $uploaded_files, true ) );

                foreach ($uploaded_files[$id] as $uploaded_file){
                    $file_name = $uploaded_file["uploaded_filename"];
                    $file = GFFormsModel::get_file_upload_path( $form["id"], $file_name );
                    GFCommon::log_debug( "Field: {$field["id"]} (multipleFiles) - {$file["url"]}" );
                }
            } else {
                if ( empty( $_FILES[$id]["name"] )  )
                    continue;

                GFCommon::log_debug( "Field: {$field["id"]} (singleFile) \$_FILES - " . print_r( $_FILES[$id], true ) );
                $file_name = $_FILES[$id]["name"];
                $file = GFFormsModel::get_file_upload_path( $form["id"], $file_name );
                GFCommon::log_debug( "Field: {$field["id"]} (singleFile) - {$file["url"]}" );
            }
        }
    }
}

add_action( 'gform_after_submission_8', 'uploads_log_after_submission', 10, 2 );
function uploads_log_after_submission( $entry, $form ) {
    foreach ( $form["fields"] as &$field ) {
        if ( $field["type"] == "fileupload" ) {

            $id = $field["id"];

            if ( empty( $entry[$id] )  )
                    continue;

            if ( $field["multipleFiles"] ) {
                $uploaded_files = json_decode( stripslashes( $entry[$id] ), true );

                foreach ( $uploaded_files as $uploaded_file ) {
                    GFCommon::log_debug( "Field: {$id} (multipleFiles) - {$uploaded_file}" );
                }
            } else {
                $uploaded_files = $entry[$id];
                GFCommon::log_debug( "Field: {$id} (singleFile) - {$entry[$id]}" );
            }
        }
    }
}