Set-up was super easy for me since I was already accepting IPN notifications from PayPal on purchases. E-Junkie send out the sales info in the same format. All that it took was a slight modification to the check for valid transaction method. This also ends up being really convenient if you add other payment processors. They translate the notifications from google checkout or whoever into the same IPN like notifications. So you only have to support one system for use with multiple processors.
Yesterday, I started using E-junkie and PayPal Pro at the C-Command Store instead of PayPal Standard. I’m happy with them so far.
Update: I concur with Brad that E-junkie’s customer service is excellent.