I called them at one point and they weren't overly helpful. In general I've found the X-Rays that Amazon ships with their books to be pretty terrible overall. Sometimes it will give a generic Wikipedia definition for a term that is specific to the book/series, which is just not useful at all.
That sort of inaccuracy is what inspired me to start making my own. Not nearly as convenient, especially when the Shelfari entries are terrible, but you end up with much better data.
Command-line xray tool
Mjwilson's Calibre Plugin