I used to work at PayPal (6+ years ago), specifically in Merchant Technical Support. Speaking strictly for myself, I hated IPNs too, and having come from anothe

I used to work at PayPal (6+ years ago), specifically in Merchant Technical Support. Speaking strictly for myself, I hated IPNs too, and having come from another payment gateway with a similarly unreliable out-of-band notification system, I was always mystified as to why folks would build whole fulfillment systems around them. I mean, I know the API-based product is more expensive, but this is your business, right? If you have any kind of significant volume, I would think the reliability of straight API calls would make the additional cost well worth it.