Good examples, but I can't help feeling that there a lot of assumptions about profitability. Dropbox, for example, is a great service, I really like it. Every tech-savvy person I know uses it, but no one I know pays for it. I know this doesn't prove anything, but it makes me wonder if they are making money. Even if disk space is dirt cheap, it's still not free for them. I wonder how many paying users they need to cover the cost of all those free users.
