I did try to manage the number of books on my Kindle, really. But this year the number has gone up; I'm now over 230. However, I keep a "To Be Read" collection to manage my reading.
I mainly read a book through before moving on, except for those times the book is absolute junk. Sometimes, I have two or three going at the same time.
I'm not tempted to give up a book because I have all the others on my Kindle. I do like having a small library with me at all times as it makes choosing the next book easier.