Seems like Ubuntu also have follow suit in the online appstore concept
For Fedora or PackageKit-powered-distros users, AppRepo project might be of interest to you, which, coincidentally, launched a couple of weeks before the Ubuntu App Directory article above.
AppRepo is powered by PackageKit .catalog file, so it is quite distro agnostic. However at the moment our contributors are mainly Fedora users, so the applications at the moment only support Fedora.
If you want to help out, we could use some help in populating the AppRepo with more apps. We choose to not use automated import to make the AppRepo a bit 'human'. If it was not added by anyone, its probably not worth looking at. So if you think theres apps thats worth to be looked at, please, add them into AppRepo and give love to it by adding screenshots and nice descriptions.
Nonetheless we are planning on an automated listing of all packages in Fedora/RPMFusion with .desktop file which have yet to have an AppRepo entry、 to aid in populating.
We also just created a GoogleGroup here: http://groups.google.com/group/apprepo.
We also have a G+ page here: https://plus.google.com/104045247598512037795