From a seller's perspective, I think Channel Advisor is a decent tool and is one of the better ones out there. I also agree with all the previous reviewers' comments.
From a buyer's perspective, stay away from their third party shopping chart. I am an eBay user first, a seller's customer second. When it comes time to checkout, I want to do it eBay's way.
If Channel Advisor meets your auction management needs, great! You have a good tool to work with. However, I get the impression that they are more interested in top eBay Powersellers. I got this feeling during eBay Live and through their other marketing efforts. Just go to their main website (www.ChannelAdvisor.com), and you will see that the only thing they promote is their Complete tool, and the only way you will find their Pro tool is if you know that the link is pro.channeladvisor.com. I won't be surprised if they discontinue their Pro tool in the near future.
Channel Advisor has failed to see that most people start out small before they become big time sellers. They should value their Pro sellers and be proactive in earning their loyality so when it comes time, their highly successful Pro sellers will become their "Complete" sellers.
Anyway, I use to recommend Mpire Builder as a better choice because it had a flat monthly fee with no listing limitations or excess closing costs, and was more robust. However, Mpire recently announced that they are officially closing their door January 31, 2007.