I remember the day I used Linux to enforce size quotas on user directories oh what a day
I was surrounded by horrible monsters wearing manho suits that made them appear superficially human... though the sounds screeching forth from their many toothed mouths in whining jarring tones would suggest otherwise and I used this wonderful feature : you can call most of the file systems commands on files !

did a dd to create a disk image specified to the correct size made an fs inside and mounted it straight into the home directory adding entries to the fstab to auto mount and setting the io permissions
It was so wonderful and the little bastards refused to use the server !