Hello - I am testing PRTG for a 5,000+ sensor deployment with one of my clients. Like the poster above, I really like the product, but the term 'DOWN' is simply wrong for the majority of conditions reported as 'DOWN'. For a ping sensor, the term 'DOWN' is OK, but for anything else it is misleading and confusing.
I have demonstrated PRTG to my client, and they hate that sensors show 'DOWN' instead of 'CRITICAL'. All other monitoring systems I sell into clients use terms such as CRITICAL/WARNING/OK rather than DOWN/WARNING/UP.
DOWN MAKES NO SENSE AT ALL!! :) A filesystem is not DOWN when it's 90% full. A printer is not DOWN if it's toner is low. A server is not DOWN if it's memory usage is 90%. The solution you gave above to only use WARNING state is no solution at all. We absoultely need the three states, it's just that PRTG terminology for the states is wrong!
Please, please, please give us the option to set these statuses to something different, or at least let us send a custom status in Notifications, e.g. give the option to translate DOWN to CRITICAL in a notification message.
If I can use CRITICAL/WARNING/OK instead of DOWN/WARNING/UP then my client will buy PRTG....otherwise they will likely go Nagios or Zabbix.