Actually, I think Dropbox has a network effect as well. I'm a paying user, but my account is more valuable to me because can share folders and collaborate wit

Actually, I think Dropbox has a network effect as well. I'm a paying user, but my account is more valuable to me because can share folders and collaborate with free users. Many of them would not use it if it wasn't free (hey, I started with the free service and later upgraded myself), but since its free they have seen how awesome it is and are 1000% more likely to upgrade to a pro plan than if they'd never started using it in the first place. In the mean time, they make my Dropbox account more valuable to me.