Hmm... actually, the IPN information isn't dependable. I've seen it take PayPal hours to send an IPN after payments. I think that generally the IPN will come in soon after checkout, but I'd be surprised if it came in during checkout consistently enough to be available for the checkout completion event. I do think the transaction ID is getting displayed on the order view screen after it's received, though, so maybe customers can just be instructed to view their order online for that info? Not ideal, I know... :-/