There is a short explanation at Wikipedia, here, another at CleftLine here, and some great resources at the Pierre Robin Network, here. Also, if you'd like to communicate with parents of children with Pierre Robin Sequence (PRS), the Pierre Robin Network also has a Yahoo! group akin to the Kids With Clefts Utah group, and you can join here.
Thanks to Amy, Jennifer, and Jamie for the resources! We will be posting more information soon!