Howto find and remove unused libraries?

[fraz <fraz@unimail.com.au>]

How can I find libraries etc that were installed as dependencies, but 
which currently have no "dependants" installed? IE the package that 
caused apt to install them isn't installed anymore.

I've been apt-getting and removing packages on my system for the last 4 
years. And I suspect there is a lot of unused crud. For future reference 
is there a better way to remove packages so the unused dependencies are 
also removed? Is "dpkg -P" equivalent to "apt-get remove"?

Thanks,
fraz