We've been adding Joom Donation as a line-item option for a payment gateway on our Joomla! sites since day 1. We only just recently were awarded a website job that needed the add-on. It was an extremely good experience. The installation went very well. I was very inexperienced when working with Authorize.net, and found that the support was extremely helpful when I ran into a snag with the recurring donation feature and Authorize.net. The developer was extremely helpful, responsive, and everything works.
Thanks for a great extension!