Steve offered a unix/linux shell script to winkle-out old files that might otherwise be missed by SAS's cleanwork utility. It's clearly a popular topic and Steve's post received a number of responses, so I thought I'd offer my own small tip.
More than one of my clients applies a quota limit to all users on their use of the /saswork file system. By setting the quota to a suitable proportion of the whole amount of space available to everybody, the quota prevents one user from hogging all of the work space and causing other users' programs to fail. For example, if you have 1TB of WORK space, you might set the quota to 500GB. It's not a silver bullet, but it works well in practice.
The Geek Stuff provides a neat "how to" on the subject for unix/linux. I imagine that a similar technique is possible on Windows too, but I haven't the experience to say so for sure.