Solution Grove is working extensively with ecomerce this summer writing a sophistocated course registration system that will be deployed for the Boston Museum of Science and at Massachusetts General Hospital. At this point we have pretty much branched the eccomerce package which is designed for selling books and other physical objects. We will eventaully refactor so that our new system and it will be a package that installs on top of the current eccomerce system.
The bottom line is I'm quite familar with the features of both systems, send me an email if you want to talk voice and I can help you answer specific questions.
For gateways we are using authorize.net. I don't think there are currently gateways written for WorldPay or PayPal.