I do most of my reading on physical books, but I have the core of my library on a Kindle as well, and where it shines is search. I can phrase and keyword search the larger part of my library. It has become an invaluable research tool. I also import highlighted passages into a database on my computer. Granted there are things like books.google.com, which I could use for search, but that's not my library. I also prefer to read on a Kindle compared to my monitor, so I regularly email large documents to it. My wish for the next Kindle is for it to be faster (more responsive UI) and handle even larger libraries.