High CPU usage

[Nemesis]

Is there ever a time when the script goes hay wire and uses all the cpu? I have a client who's site was suspended due to high cpu usage. The server admin said it was affecting everyone's sites, as I did have some pm's on sites being down, and he went ahead and suspended it. Not a problem as I can reinstate it, but don't want it to happen again. History has a few hundred of these "Updating disk usage in my sql"

I currently have 42 clients sign ups/emails and 25 sites right now remain active. No other sites having these issues as i have been checking the logs. And I am no where near over capacity on this server. so why did this one site use up all resources a few 100 times in a day? And what should I do reinstall the script?