Debian's snapshot archive is a collection of every past and current Debian package searchable by name and version number. Perhaps a dist-upgrade has messed up a package and a fix is not readily available? It is possible courtesy of this archive to download and install a previous version.
Example: I am using the latest 64-bit kernel offered by Debian linux-image-3.12-1-amd64 and I can find all the previous linux-image-VERSION-ARCHITECTURE packages at http://snapshot.debian.org/binary/?cat=l. If I click on my kernel package it lists the different versions available and I can select a deb binary for download and install with dpkg -i linux-image-*.deb.