I did the exact same thing a year back, except for the books. Spotlight for the searching, Dropbox for the backups and an scansnap for the pdfs. It's working great, whenever I want to look something up I just search for the key words and there it is. It's a pity there is no search functionality in the Dropbox site. I don't think I'll part with my books though, but being able to search through them would be awesome.