I pretty much sell all my comics through their consignment services. Overall, I have been very pleased with their service. The fees are reasonable and I don't have to mess with the hassle of shipping the book to a buyer (which presents another host of potential problems).
My only complaint is the time it takes for them to actually list the books. I just sent in two books for consignment, and it took them around a week to get them scanned and ready for me to set the price. I understand that they have to scan the book and then file it, but if there was a way they could shave a few days off the process that would be great. But I'm nitpicking.