This is one area where Netsuite has really done well.  With the ability to customize the email message, this feature has become invaluable.

I can think of a hundred uses for this feature.  From contacting external customers based on a criteria to alerting our staff to internal issues.

The one I am working now is for our internal staff.  I have a saved search that looks at a custom "in stock" field (we dont use the NS stock field) and checks to see if we have the item available in our warehouse.  So if someone mistakenly marked an item as being on back order but we have some in our warehouse NS will send an email alert to our customer service email address.  The email then tells them the proper workflow so they can correct their mistake.  It's a great way to check that workflow is being done