As for many of us search books on internet but most of them can not be downloaded but now Google Book Search a unique place to search and read your favorite books before actually purchasing or to take reference from that book for your documents.
but while searching books you can’t download copy write Books from Google Book Search. A several restrictions are enforced for preventing downloading of copy write books so you can only read some pages from that book.
now here is a smart utility that let you save book as PDF from google to your local filesystem from google book search that is Google book downloader .
instruction for installing: for download or install any software or tool one must need to fulfill the hardware and software requirements so for google book downloader Microsoft .net Framework 3.5 SP1 is required.
Google book downloader description : http://www.codeplex.com/GoogleBookDownloader