I'm not sure why they removed it either; so I wrote a little script that helps you monitor disk usage. It is open source software, that uses Python and GNU tools to do the work. I've been looking for people to test it. If you have the time, please try it out.
While it does not set hard limits, it will notify you via email if a user is above their quota for an extended period of time (it will notify the user right away). This gives the user flexibility and time to get their disk usage back under control. The goal is to allow users to continue working through fluctuating usage, and only involve administrators only when necessary.
I did include fairly thorough documentation, which should show you how to get started. If you run into any problems or notice any mistakes in the instructions, please let me know