Most customers won't complain.... (Score 1)

It's been my experience working on the ISP side of the world that just about every ISP / colo provider claims at least 99.9% uptime with every SLA (service level agreement).

Its pretty safe to say that almost none actually back that up with their performance. However, from my experience, very few customers will try to get the company to honor its SLA because you need to provide pretty good documentation. We had a few situations where the company was down for a few hours, dropping its uptime below its guarantee, and still wouldn't credit us because they claimed the downtime to be much shorter. No matter how many traceroutes from major network nodes we showed, they kept arguing against it until we gave up.

Also, unless there is a catastrophic downtime that pulls service out for more than a few minutes at a time, and uptime falls below 95% for the month or lower, most users don't want to be bothered fighting for a credit. If you've ever dealt with any big telco / network provider you know what I'm talking about.

So, the bottom line is that in a lot of service industries (internet especially) it is very easy to claim 5 9's reliability, come close, and not really pay a huge price for failing. In fact, most people won't even notice. Now, for the 911 network, air traffic control, etc., it's a different story.