How to get custom product line item text field value?
I ended up doing the following : 

    function my_Module_form_alter(&amp;$form, &amp;$form_state, $form_id){
           if ($form_id == 'commerce_cart_add_to_cart_form_12'){
                  dpm($form, 'cart form'); //to use with deve module   
                  $form['#submit'][]=('my_Module_commerce_add_to_cart_form_12_submit');
                  }
            } 

       function my_Module_commerce_add_to_cart_form_12_submit($form, &amp;$form_state){

             $user_text_temp=$form_state['values']['line_item_fields']['field_license_details'][LANGUAGE_NONE][0]['value'];
             dpm($user_text_temp, 'extract value is ');
            // whatever else you want to do with that user_text_temp value
          }


I think that's the easiest way to do what i want. I posted it because it may be of use to people new to drupal.