For the most part, we're taught from a young age to try and work well with others. Sharing, caring, and not hogging all of the spotlight is generally in one's best interest. So much for that.
Yahoo has announced that it will cease letting users login to various services (including its popular Fantasy Football and photo-sharing Flickr
sites) with anything other than a User ID from Yahoo. Previously, users were allowed to login via their Google or Facebook profiles -- a fairly standard practice across the Web. Creating a new ID for each site can be a hinderence, and enabling people to use logins that they already own would (in theory) create less friction to signing up, thereby increasing the user base.
Evidently that math isn't working out so well for Yahoo, with a phased rollout to require users to establish a Yahoo ID if they want to continue using select services. It's no doubt difficult for a service to support multiple sign-in options, so it's possible that the change will enable more customized experiences. Still, it feels pretty raw for those who already signed up using an alternate ID.