From Raspberry Pi.org:

This disc image is not the one we expect people to be using as standard (that’s from Fedora, and has some other exciting stuff bundled with it, which we hope to be putting up over the next few days). It’s the Cambridge reference filesystem, which is a fully functional Debian Squeeze installation containing LXDE and Midori (browsers); development tools; and sample code for accessing the multimedia functionality on the device.