After an upgrade from Lucid to Precise, my PHP install started complaining about a library:
PHP Warning: PHP Startup: Unable to load dynamic library '/usr/lib/php5/20090626+lfs/gd.so'
While I've got a hunch that the actual problem is related to issues I had during the upgrade, turning this error (and other similar ones) off is as simple as going into /etc/php5/conf.d and renaming the file, in this case gd.ini to something like gd.ini.bak.
This, along with an apache restart, fixed things for me, at least temporarily.