Have used them three times and will be using them again next month.
They are basically a discount bike shipping broker for FedEx (and possibly other services). Once you purchase, they email you a shipping label from the carrier (never had them use anyone other than FedEx) 10 days before your scheduled ship date and you take it from there. If you bike goes FedEx, you can even drop it off at a FedEx/Kinko's location and save the $5 pickup surcharge. (The LBS I have pack my bike is around the corner from one such location so the guys there walk the bike over there after packing it.)
The one thing I don't like about the service is the 10-day thing. That's fine at the start, but if you are on tour for longer than 10 days you cannot get a return shipping label before you start the tour. That means you have to find a computer with a printer at some point to print the return shipping label. For me, that has meant having to make trips to local libraries in Missoula and Rapid City on the last days of tours. Fortunately, I have finished tours on days and at times when they are open, but it's still a bit of a PITA.