A couple of months ago I claimed "These days it doesn't make much sense to build a consumer site with its own private account system" and released a Ruby template that showed how to rely on just Facebook and Twitter for logins. It turns out I was wrong! I always knew there would be some markets that didn't have enough adoption of those two services, but thought that the tide of history would make them less and less relevant. What I hadn't counted on was kids.
My Wordlings custom word cloud service has seen a lot of interest from teachers who want to use it with their students, but especially amongst pre-teens, there's little chance they're on either Facebook or Twitter. They may not even have an email address to use! Since that's not likely to change, I added a new "Sign in for Kids" option that just requires a name, skipping a password even. It has the disadvantage that once you log out, you can't edit any of your creations, but that seems a small price to pay to make the service more accessible.
Pete Warden's blog 