[eluser]MikeHibbert[/eluser]
Well theres always the option of NOT using ajax but instead checking when the page is changed or refreshed.
Thats not so bad if you imagine the user going from page to page o even from the current page to the checkout.
The CURL method is fine and you should be ok, its just another way of doing the same thing and you can set the confirmation URL and get the confirm URL to update the status in the database. Then when you refresh or change page you can see the status of the transaction then, you might even send a confirmation email if you think its worth it.
Mike