A Google Book Search user is upset that Google has dropped the search within your Google Book Search library feature. He expressed his complaints in a WebmasterWorld thread. He said:
Then a couple of weeks ago, I logged in and I can no longer restrict my search results to items in My Library.
For me, this is the primary way I use Google Books. First search my library. If I don't find it, search more broadly. If I find something good in general search, add that book to my library. If you will, it's like manually controlled personalized search.
It's true, I do not see a way to search only my library, even within the advanced search feature.
This must have changed when Google updated the My Library feature in late January.
Forum discussion at WebmasterWorld.