Print Release System provides Web-based management of System V printing. It sits between Samba and the System V printing system. It ought to be relatively easy to make it work with other printing systems. After the job is printed, the user needs to consult a Web page that shows their queued jobs, which can be selected and released for printing (or canceled). A record is maintained for each job and, once the user reaches a quota, they can't release any further jobs to the printer.
If you have a pre-determined quota from your operator of how much packet data you can use in a month, it's a pain to first find the Logs application, open the packet data counter, then try and work out how much data you have left from the amount used so far. Data Quota shows two simple bars: one showing how much of the data for this month you have used, and one showing how much of the month has elapsed. This lets you tell at a glance if you've been using data up too quickly or slowly, so you can be more (or less) frugal.