I wish we had implemented one of them. I sent out an RFP, got responses, and was ready to start evaluation process. Then management decided to pull the plug on the project, shooting a nice hole in my credibility.
I don't know if any of these companies is an Oracle/JDE partner (K-Rise is an IConsortium member, I believe), but they all have pre-built connections to JDE, which was one of our requirements. There are certainly other shopping cart applications available, but we have no interest in re-inventing the wheel on the JDE side.
Sorry, nothing of substance to offer regarding experience with any of the products. Maybe when we decide to join the 20th century, (I know, it's the 21st century -- one century at a time, please) I'll be able to speak to the experience/pain issue.