After many comments about it, I've decided to make a separate post as it seems everybody wants to know what theme this is even though there was an announcement on ppa.webupd8.org.
The theme in the above screenshot is Bluebird GTK (the default Xubuntu 10.10 theme) and a new Bluebird Metacity theme - I've combined these two and created one package which you can use in Ubuntu (Gnome) by adding the WebUpd8 themes PPA.
I've also fixed a small bug in the GTK theme which made the Nautilus Elementary zoom slider to look broken.
Install Bluebird GTK + Metacity in Ubuntu
Bluebird is available for Ubuntu 10.04, 10.10 and 11.04. Add the WebUpd8 Themes Ubuntu PPA and install Bluebird GTK + Metacity using the following commands:
sudo add-apt-repository ppa:webupd8team/themes sudo apt-get update sudo apt-get install bluebird-gtk-theme
If you're not using Ubuntu, get the GTK theme from Github and the Metacity via Gnome-Look.