Furfly has several ecommerce sites running successfully, but they are based on ACS 4.2 Classic, using the original ecommerce port. This probably doesn't help you much as OpenACS and ecommerce have both changed considerably since then, this is about as much encouragement as I can provide.
Berklee Music is also using it; we did that work sometime in 2002, so I'm not sure what version that was, but it was working ok at that time.
