I keep my cell phone next to my ear when I go to sleep. It is set to send out a piercing whistle I get an email from a particular address, which indicates that my website has been unavailable for 15 minutes. That whistle has gone off exactly once. (Credit more to Slicehost and my software stack than to me.)
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.