I am still a lurker on the GR Librarian forums because I never know when a great tip will pass my way. Like this thread where I found out about a link to use to search all of Gutenberg's books!
I am SO wildly happy about that. Because when I quote I like to also give a link to the full text so it can be read in context.
So many people love to share quotes but often don't stop to realize that yes, those are wonderful words from Famous Author - but no one has any idea where those words were used. Since you loved them, you want to go read more, right? Oops, except there wasn't any source quoted, just the quote and author's name. So if you're making the jpgs and gifs for a beloved author? Please add the source? Meanwhile the rest of us will spend time trying to track down the book, because often quotes make me want to read more. And sometimes it's much more enlightening to read the quote in context - because the author could be taking the idea in a completely different direction than you'd assumed.
That's why I love the ability to search Gutenberg, because I've often tried to track down a particular quote using that site. Except I've been going into each book and using the Find in page option, so that new (to me) link should speed things up. Now I just need something (public domain) to search for...
Oh and a great place to check for the sources of popular quotes: Quote Investigator. They're really through.