/var/lib/apt/list/partial eating all of the disk space.
 

Girlfriend was telling me her laptop wasn't working anymore. During boot I noticed root was complaining it was full. After some searching, I found that /var/lib/apt/lists/partial was full of *.FAILED files, many 32GB in size, taking up over 9GB in total.

Any idea what could cause them to be so large and so many?

i've seen a topic about this very recently, either here or on crunchbang forums.
sorry i can't help more, but i'll post again as soon as i find it.