Automatic Directory Size Monitoring on Windows Machines

I think the limiting factor to this is that it typically puts a pretty measurable load IO load on servers when you walk their entire file structure, and it takes a while to run.  To give yourself a sense of it just open treesize or similar on a server and see how long it takes before it actually finishes the scan.  Few things makes an sysadmin more annoyed than when the monitoring tool bogs down the monitored server.  Probably could be handled relatively efficiently with the agent if they did decide to go that way.