A few days ago Canonical presented an innovative new feature for Ubuntu called Web Apps. Web Apps integrates websites with the Ubuntu desktop making them look like native desktop applications. For example you can control Grooveshark through Ubuntu's sound menu, receive native Facebook notifications, search your Google Docs via Dash and much much more. Here is a video describing the Web Apps feature.
To install Web Apps in Ubuntu Precise Pangolin 12.04 and Quantal Quetzal 12.10 open a terminal and type:
sudo add-apt-repository ppa:webapps/previewsudo apt-get updatesudo apt-get install unity-webapps-preview
Log out and back in to Unity and the Web Apps feature will be automatically enabled. All you have to do is open Firefox or Chromium and start browsing. If a website supports Web Apps feature you will receive a notification on whether you want it to integrate with Ubuntu. For example you can try Gmail, Yahoo, Facebook, Twitter, Grooveshark, LastFM. Soon I will publish a list with all the supported websites.
Some services like Facebook, Google (including Docs, Gmail, Google+, Picasa and YouTube), Flickr, Twitter, Foursquare and Identi.ca will be directly integrated into Online Accounts.
Have in mind that Web Apps is still under developement, therefore it may have many bugs. This feature won't be backported officially to Ubuntu 12.04.
To remove webapps open a terminal and type:
sudo apt-get install ppa-purgesudo ppa-purge ppa:webapps/previewsudo apt-get remove gnome-control-center-signon signond signon-keyring-extension signon-plugin-oauth2 signon-ui libunity-webapps-chromium unity-chromium-extension unity-lens-gdocs unity-lens-photo unity-scope-flickr xul-ext-webaccounts xul-ext-unity xul-ext-websites-integration
Then log out and back in.