I also ran into this problem spontaneously this week.
I thought that it was related to loading yet more books onto my Kindle because I've been having trouble for a while with collections @ ~990 books and ran into this problem after mailing new docs to my kindle...
Symptoms were "Your Library" not working.
After reboot either a blank page with control toolbar visible or 3 documents from the library visible depending upon what mode the home page is configured for.
Books could be accessed only by clicking a search suggestion. Search itself didn't return books.
I was just steeling myself to do a hard wipe when I found this forum post.
