If I'm not mistaken Ubuntu is based on a snapshot of Debian sid (unstable) Trying to grab packages from the Debian repositories would probably give you OLDER packages than what is in the Ubuntu repositories and will at some point probably break your Ubuntu system.
Use Ubunutu repositories for Ubuntu.
Use Debian repositories for Debian.
Originally Posted by wikipedia
Ubuntu packages have generally been based on packages from Debian's unstable branch: both distributions use Debian's deb package format and APT/Synaptic to manage installed packages, although Debian and Ubuntu packages are not necessarily binary compatible with each other.