At least half of the books I read are hard copies from the library. I have been an avid library user for most of my life and honestly couldn't imagine giving it up. And I love books, I like to hold them, flip pages back and forth when I want to check on something and sometimes sneak a look at the end.
However, I read a lot. Really a lot. For me to lug around books on vacation, waiting rooms, to work for reading on my lunch hour or to events/places where I know I will have down time or get bored with the activity is just not feasible. So the Kindle is my choice when I want to have books available but not be bothered with the weight or the space that multiple books take.
There is also the $$ factor. Most of my Kindle books are freebies or very reasonably priced. Best sellers and speciality books in Kindle format can be expensive so picking them up at the library just makes sense for me.
The Kindle will never replace books for me but when you want multiple titles, lightweight and convenience, the Kindle rules!