Earlier quoted context omitted.
I agree. That's why we don't do uptime monitoring, or any kind of monitoring really. PagerDuty is an alerting system which plugs into any monitoring system (Pingdom, Nagios, Cloudkick, etc) and alerts your team via phone, SMS and email when problems are detected. We add advanced alerting features, like 2-way voice and SMS alerts, automatic alert escalation, and on-call duty scheduling to these existing tools. You're…
>> "PagerDuty is an alerting system which plugs into any monitoring system (Pingdom, Nagios, Cloudkick, etc) and alerts your team via phone, SMS and email when problems are detected." Pingdom already does that. I'm not clear what you're offering here...
Actually, Pingdom is one of the most common services used in conjunction with PagerDuty.
At a higher level, what we're trying to provide is an on-call management and alert dispatching tool. What PagerDuty does is let you control who, how, and when people are notified when problems occur. In contrast, monitoring tools like Pingdom and Nagios focus more on detecting problems. While they have some native alerting functionality, we think with PagerDuty's advanced alerting, they can function all the better.