The plan is to make it more "convenient for Ubuntu users and community members to access information, communicate, and contribute." It'll replace the Launchpad login service, but don't worry -- existing Launchpad accounts will still work with the single sign-on service.
Over the next few months Canonical plans on shifting the entirety of Ubuntu and Canonical related sites running Launchpad and migrating them to Ubuntu single sign on. It's a bit ambitious, and Canoncial is going to start obviously, with their own sites, and then work with the community sites to get the transition done.
Canonical doesn't want to make this hard, though, so Launchpad data will be copied over to the Ubuntu service during the transition. However, once you've signed into the new Ubuntu account and the transition becomes complete, your Launchpad one goes defunct. Both sites will use identical credentials, and while Canonical has noted this isn't ideal, it's necessary.
Here's the added bonus in the transition. Ubuntu single sign-on is build on the OpenID standard. That means any site that accepts the standard will let you pop on with that account name. That's actually kind of nice.
And why all the fuss?
The Launchpad login service has served us well for several years but Launchpad is not a familiar brand for many Ubuntu users. As Ubuntu grows, we’ll see more and more users who don’t understand the connection between Launchpad and Ubuntu and the new Ubuntu login service is intended to overcome this problem. It will also enable us to develop features which are more oriented to Ubuntu users.Interesting. A small shift or a big change? In this case, conformity and uniformity seem to be good on the whole. I'm all for tidying up and simplifying the login situation.