Although I've had a few that I ended up not using in the past, I have used most. I just tend to be thinking several projects ahead and want to be prepared. I currently am developing three at a time and as one is making a bit of money, I'll move on the next one. At times I have sold domains, both developed and not, when I want to do something else. I don't register very esoteric names but specific keyword combinations so they usually sell well when pointed out to the right person.