Hello Julia. I purchased my Kindle in mid-February. I keep a list of each book I read, so I can look at my list and see that I've read 26 books on the Kindle and 28 in paper since. I have a huge stack of TBR books here in the house and I'm an active book swapper, which means I need to read and mail a certain number of paper books each month. I'm using my Kindle as a substitute for hardback books I would have gotten from the library and for those classics that I want to read and should have read, but never got around to. Well, not entirely true, since I'm satisfying my SFF itch with books from Baen, Charles Stross, and Steve Jordan. Since you like SF, check out Steve's books at
http://www.stevejordanbooks.com/