I have about 60 books on one of my Kindles. The rest have 20 to 30 books each. I need to clean up the one with 60 books but I've just put it off. It's too many books. It makes browsing clumsy. Also I have 3G so it's trivial to download any book any time.
That said, I put the entire Dropbox collection on my new Nook Glowlight 3. That's 518 books. I put books into my Dropbox collection so I can browse through them easily on my phone wherever I might be. It began as a backup of favorite books and has turned into my primary library of late. And now the whole thing is on my Glowlight, probably just as an experiment but I'll see.
It does make browsing my library on the Glowlight difficult. I can find what I want by searching if I know what I want but if I don't and I just want to find something to read I'll look at a book, look at a few more and then want to take another look at one a while ago and if I can't remember the title or author my odds of finding it again are small.
Still, it really is a nice feeling to have so many wonderful books all in one device that fits into my pocket. And if I get hit by a bus maybe it'll go to heaven with me and I'll have plenty to read there, and, according to rumor, lots of time to read them.
My guess is that I'll pare it down to 30 or 40 books in time but who knows!
Barry