Bleagh

for many businesses e-mail is mission critical, but if it's up between 9 and 5 it could be down the rest of the day and not matter. And if it is down during the day and business is crippled, it hurts, but the business doesn't go under.

I can't think of very many companies that electrical power wouldn't be considered "Mission Critical", but very few companies (outside of ones focused on Internet accessible servers) have backup generators and UPS systems, and those don't come anywhere close to 7 9's of availability.