How do you limit the use of network storage in your company?
This is one of those areas where my views are contrary to the mainstream. We do not have disk quotas, in fact we encourage users to get data onto the servers and out of file cabinets. We have been doing this for a while, in preparation for implementing document management.
Disk is inexpensive, and has been for a while.
None of the alternatives is more palatable to letting home folders and shared folders grow. If users have disk quotas, they are either going to save data onto their local drives, find other places on the network to hide it, or print it and stick it in their drawers/files.
We do regularly monitor space and usage, and work with users who are getting out of control. We can help them archive things to DVD and/or to triage when necessary.
We take this approach with email as well. We have an archiving solution (old mail to an archive server) so the disk space on the email server is not out of control. Only a couple of users are really a concern anyway, and we can work with them.
EDIT: Reading other answers and comments, a question comes to mind .. should we force the business and the users to cater to our convenience? My view is that we should cater to the business as much as possible, which is why we operate a "quota-free" environment. Our role is to support the business, not the other way around.
I was a sysadmin at a school and all students had network accounts. I wanted to encourage the use of computers so I removed the quota limits on the home directories. For most students this went well but some filled up their directory quickly with gigs of video and mp3.
Contrary to what you expect this wasn't pirated stuff but their own video footage and music from the school band.
So in the end I only needed a script which made up some nice statistics of the file usage, if a home drive was filling up more then ten times the average I would have a look at it and suggest a better way of archiving. Mostly this was just a list of the biggest files and last access time. Really misbehaving students would be put back into quota but that situation has not risen during my employment there.
We use the default Microsoft quota system on the file servers, specifically when it comes to home drives.
Other than that, one of our admins down south of us has a tendency to let the users' project spaces fill up, then encourages them to run duplicate finders and large-file/last-accessed programs such as "Doublekiller", "Easy Duplicate Finder" and "JDisk Report", which is one of my personal favorites.
Another solution we're looking at implmenting is Symantec's "Enterprise Vault" especially if you're doing disk-disk-tape or have the tape storage available to shuffle files off to.