I originally bought a MyBook with the intention to do backups of a few PC's on my network. I wanted to mount the PC's onto the MyBook and then use rsnapshot to pull the backups from the computers. It took a while to get a buildroot to successfully compile, but finally I managed to compile it and also compile the CIFS module for the MyBook kernel.
Getting to the point, I found quite a lot of valuable resources on this site so I thought I'd share my work. Have a read about it here. I am still in the process of testing eveything, but so far it seems pretty stable. If you want to setup rsnapshot and a backup schedual, I can try to help, but really all I provide is the kernel module and instructions of how to mount it.