Some say - paraphrasing Clarkson, some say ...- that Google has services for everything, and that being the case they could not put books aside with Google Books, a utility to read books - or extracts from them - online.
The problem is that the facility to download them does not exist, so you have to resort to alternative solutions such as this application for Mac OS X: Google Book Downloader.
There is not much to explain as the operation is incredibly simple: We put the ID of the book in the text box, we choose where to save the PDF and wait a while.
Of course, be careful because it seems that if it is used a lot from Google they ban the IP, although that for those of you who have dynamics is not a big problem.
Link | GBD