Dont use the quota system, everytime a user uploads a file, the quato
system gets called. It is not efficient. Having come from an ISP
background, I can confirm that the best way is to run a script nightly
adding up usage.
You can run this script as often as you wish (obvious not every minute),
and then check whos dir structure is changing. And then run another
script just on that one users.
If you are worried someone may hit you with 1gigs worth of data, and use
up your drive (it has happened), then put a block in on the directory
change size of say 100Megs, per nite. If a user wants more then they
will have to email you, but most users will not even realise that the
[article about quota snipped]