Apart from a very small number of my very favourite books I don't re-read. I don't like to re-watch films either, while listening to music is a different thing for me, so re-listening to a song isn't really comparable.
I've always been more of a library borrower than a book buyer anyway, though since getting a Kindle, I have bought more than I ever used to. But while I read very few library books now, I read a lot of the freebies on Amazon instead.
The reason for keeping my books is mainly so that I know I've read them and don't start to read them a second time, as my memory is terrible! Just knowing I've already read a book even if I can't remember exactly what happens is enough to put me off.
In saying that, I have enjoyed re-reading a handful of really good books and can appreciate people liking the familiarity and the idea that it's a bit like revisiting an old friend. At the same time, there's so many new and potentially great books out there it seems a shame to spend too much time on something you've read before...
As for DRM. Even before I had two e-readers I removed the DRM from my books so I'll be able to read them on whichever ereader I happen to own at the time.