There was a massive Skype outage recently, lasting about three days. It remains to be seen if/how emergency calls were affected.
But as we rely more on Internet-based communications systems for things like medical records and emergency communications, reliability will move up the list of desirable features closer to the top. Let’s just hope that the Internet can stand the strain.
Basically, don’t replace your landline or cell with Skype. I don’t think anyone should rely on cellular technology for their 911 service either, but that’s another argument for another time.