[shabble]

I often find myself looking for the opposite mapping; to which package does /usr/share/foo/bar.blob belong?

   $ dpkg --search /etc/apt/
   debconf, apt: /etc/apt

[__david__]

I prefer "apt-file search" which is much faster than "dpkg -S" at the cost of some disk space and having to periodically do "apt-file update".

[ars]

apt-file search is [also] for uninstalled packages. If all you care about are packages actually installed use dlocate