"...The only situation I can think of using a control chart for capacity is if you had a piece of equipment that if over utilized would cause damage or premature wear in which case you would only have an upper control..."
I disagree. My system (SEDS) has a special part (updated lists) called "Unusual Capacity Usage OUTSIDERS" that can help to capture some serious issues with servers, such as database going down, LPAR migration out of a host and other unusual capacity releases, that are not necessarily good things:
The following control charts from my up-coming CMG'09 workshop presentation are good illustrations of those type of finding SEDS captures:
1. Vmware host issue (VM migration):
2. Unisys server database is down:
3. Mainframe application unusual low CPU usage: