That would be cool. Personally if I ever want a quote I want a motivational one so that I can stop goofing around and do some work. Maybe something that works out what sort of quotes I do / don't like would be a cool feature
Exactly, saving quotes will be nice. Also i think, in the far future it could be a hub for books. As a social network. Maybe it is a silly idea, i don't know :)
You could always suggest the book that the quote is from for purchase. Once you have built a user base it could be worth reaching out to book shops for some form of partnership (or for them to buy the app outright).