It all depends on what the SLA says, but hypothetically, if they are down for 24 hours a year, that's 99.7% uptime, which isn't terrible. Heroku had a 1-2 hour outage the week after we switched an app there last year. My boss was freaking out, cursing about how they were unreliable, etc, neglecting the following: 1. The timing was unfortunate, but that was the first outage in months. 2. We had had multiple outages on…
Uh... 99.7% is ridiculously bad if you're doing anything that matters.
Internal examples:
If shadowcat's public facing website is down for a day, a few people can't read blog posts and maybe we'll miss out on a potential customer - but our existing customers will be entirely unaffected.
If our ticket tracking system is down for a day, it'll annoy the hell out of the existing customers but we can still get the work done since they all have direct email and IM contact info for people.
On the other hand if our ircd is down for an hour, it's time to panic, because that massively interrupts our ability to co-ordinate our work.
External examples:
If linked in is down for a day, I don't care - anything I do on that can wait until tomorrow.
If duckduckgo is down for a day, I am going to burst into tears because I use it all the time for information I want -now- and going via google is substantially more annoying.
So "anything that matters" is really quite relative.