The new Ubuntu 10.10 Maverick Meerkat "Extras" (http://extras.ubuntu.com/) repository is now live. This repository will hold new post-release applications.
New post-release applications?
This repository will not hold updated versions of the applications already in the Ubuntu repositories. It was built to hold completely new applications so users don't have to wait for a new Ubuntu version to install an application which just came out (application, not new application version!).
That means the Ubuntu Extras repository doesn't have any purpose until after the Ubuntu 10.10 Maverick Meerkat final release.
The new "extras.ubuntu.com" repository was planned to be added to the default sources.list starting with Ubuntu Maverick Meerkat Alpha 3 along with a prototype UI in the Ubuntu Software Center - so the new apps are easily discoverable. The Ubuntu Software Center got the "What's new" section, but the repository has not yet been added to the default Ubuntu 10.10 sources.list (which obviously means that the apps under "What's new in USC are not the ones in the Extras repo yet).
Besides the obvious advantage this brings to the end users: they get to install new applications without upgrading to newer Ubuntu versions and without using a PPA (and instead use an official, 100% safe repository), there's also one other big advantage: the developers don't have to release their applications in time for the Ubuntu development which could mean less bugs, more attention to details.
All the applications in the new Extras repository will be synced from a PPA (which you can add if you want to have these applications a little bit sooner than the Extras repository).