There are some debian tools to deal with "orphaned" packages, like deborphan. Its usage is pretty simple:
# deborphan
.. follows a list of "orphaned" packages
I find more interesting the utility named "cruft". I use it like this:
# cruft -d /usr/lib > report.cruft.txt
This checks for files that must be in the system and files that should not be in the filesystem.
# cat report.cruft.txt | grep libGL
/usr/lib/FGL.renamed.libGL.so.1.2
/usr/lib/libGL.la
/usr/lib/libGL.so.180.44
/usr/lib/libGLcore.so.180.44
/usr/lib/xorg/FGL.renamed.libGL.so.1.2
These files should not have been there. So, I can delete them.
I'm not aware of all the options yet, but I'll look into it when I have some time to spend...
It's convenient to check what package provides some file:
# apt-file search libGL.so.1
fglrx-glx: /usr/lib/libGL.so.1
fglrx-glx: /usr/lib/libGL.so.1.2
libgl1-mesa-glx: /usr/lib/libGL.so.1
libgl1-mesa-glx: /usr/lib/libGL.so.1.2
...
Also, you can use dpkg:
# dpkg -S libGL.so.1
