A number of projects are using Debian Live:
gNewSense "forked" a very early live-package
GNUSTEP Live CD using live-package
PlayStation 3 Live CD using live-package
Sidux Live CD "forked" an early live-package
Clonezilla (system image distributer)
Xorcom Rapid live cd - Asterisk-based live CD
PelicanHPC uses live-helper
IES S'Arenal, Llucmajor (Secondary school located near to Palma de Mallorca), Spain.
pure:dyne: Providing a live system and a software repository for media artists.
Privatix Live-System: Debian based german live-system for privacy and encryption.