How does hosting it yourself protect you from these issues (downtime)? The only thing you gain is control over the situation, which may be a worse prospect if you don't have the same level of resources that Google/whoever has to fix it.
You know who got blasted out of sleep at 3 AM because my email was down? I don't know, but it sure as heck wasn't me.
I did too, and I didn't get much sleep in those days.
Only people who were unfortunate enough to be working on the GMail team from UTC+7, perhaps UTC+6, instead of in Mountain View.