In Ubuntu we receive a multitude of package installation failures due to people misconfiguring their /etc/default/grub file. During this release cycle we plan on putting some work into helping people resolve these misconfigurations and subsequently we need to understand what changes people make to /etc/default/grub.
Fortunately, the grub apport package hook includes /etc/default/grub in the information that it gathers and uploads to Launchpad. So we just need to get all those attachments from Launchpad. Sometime ago I did this for the X org team with xorg.conf files and used the Launchpad API directly. However, now we have lp-grab-attachments, part of the lpltools package, which can make this much easier:
lp-grab-attachments --package grub2
Now I have a bunch of /etc/default/grub files on my local system and I can use grep to search them locally. The most common errors all related to quoting as we had expected. People either neglect one of the quotes in the pair or use unicode quotes instead of ASCII ones.