I am currently completing an update of my e-book collection. I have over 3,000 titles. I've been reading books in digital format since 1997. I read a lot. I always have.
I use Calibre on my home computer to manage my books. There is no hand held e reader that can manage that many titles. Especially since I don't get them all from the same place. How could I? I was reading e-books before Kindle was invented!
This means, like all competent librarians, I must spent time sorting through my collection, marking groups, making titles and authors make sense and making sure that I can find the book that I am looking for. I have discovered that by tagging my books, I can sort through them easily and find books on the subject that I'm interested in. But taking the time to tag 3,000 books? Not so wonderful. I do it one author at a time. That way, I can frequently apply tags in groups.