i stupidly started a rather nasty thread at the beginning of my apug-posting about the topic and i'm somewhat glad google is taking care of it now. i'm quite surprised that there are so many photography themed books digitalized by them (or are they just doing so much of them and i'm only looking for the foto ones?).
it's really great. there are books on pretty much everything: collotype, copper printing, old photo manuals on pretty much any classic printing techinique...
on the other hand, i'm not really happy that google is doing this... just another thing for them to make a profit and take over the world, ahem... the internet. i'm all for making books out of print accessible (their authors long gone...), but i definitely have mixed feelings about google forcing them to. buti'm very happy that someone finally takes care of all those out of print books.
reading on a screen is very much annoying. i take buying a book or getting it from my local library over a pdf or the google screen version anytime. but coming from the (german speaking) middle of europe, there's only so much you can find in the libraries. and even if, if it's not in the main library, you have to beg the librarian if you can take the book home or otherwise you have to read it there ... or make analog copies (no one minds that).
everytime i have the "darkroom" books from lustrum press in my hands (the first one, more than the second one), i think about what a shame it is that those are out of print.
another good non-google source for a few old books (i posted it here before):
http://chestofbooks.com/arts/index.html