Any time you put your eggs in one basket you're setting yourself up for potential problems. Use Pingdom, but then add in either a direct competitor or someone else like Keynote or Gomez (no endorsements of any of the above by me, by the way). Then when one goes down, there's only momentary panic, and when they're all going off, you can panic for real.

I wouldn't jump off of Pingdom because you think someone else is good. Unless that someone else can provide some pretty hard evidence, their architecture may be just as susceptible to a hardware failure as Pingdom.

I would expect Pingdom to write up a report on what happened and write up what they plan on doing to prevent it from happening again. I don't see it anywhere on the Pingdom site, yet (I'm not a customer).