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Here's another entry in my irregular series entitled "How to be Evil" which is directed at nobody in particular.
First, create a web site which becomes popular. Actually making this happen is left as an exercise to the reader. If you can't create one, then buy one that is popular and proceed to the next step.
Second, start adding a bunch of glop to the interface. Make it do things that are good for you but aren't good for your users.
Third, offer a way to disable some of the glop by providing settings which can be adjusted through their "popular-web-site account".
Fourth, watch as everyone has to sign up for an account in order to get things back to the way they liked it.
Fifth, claim your web site is growing like crazy because all of these accounts keep being created. You don't have to mention WHY this is happening. Just let the readers assume it's due to compelling content or something.
Sixth, frolic in filthy piles of cash as the ads roll in.
Somehow, I have the feeling this has already played out a number of times in recent history.