Who's using Clutter?
GNOME Shell
GNOME Shell, the base of the GNOME 3.0 user experience, is based on Clutter. Screencasts are available.
Media Explorer
The Media Explorer user interface, developed by the Intel Opensource Technology Center, uses Clutter (and other GNOME technologies) to browse and play media on local and networked devices.
MeeGo Netbook User Experience (UX)
MeeGo's netbook UX makes extensive use of Clutter:
litl webbook
Most of the litl webbook user interface is written in Clutter (plus liberal dashes of GNOME and other open source software: see this blog entry and this other blog entry for more technical details.
Photos & Mediawall from asklitl on Vimeo.
GNOME Games
Several of the GNOME games have been ported to Clutter, including Gnometris, Lightsoff, Nibbles, and Same GNOME.
See this blog entry for more information about the Nibbles port.
Chromium OS
Chromium OS, the open source project underlying Google's Chrome OS, incorporates Clutter for window animations. See the Google Chrome OS in action:
Maemo 5
Clutter is a significant component in the Maemo 5 user interface framework. See this blog entry for more details.
Moblin UX
The Moblin UX used Clutter. The video below shows the Moblin desktop (based on Clutter) in use.