"It wasn’t a good week for a number of Office 365 users in North America this week. On Monday, June 23 Lync Online was down for a number of usersfor several hours. On Tuesday, June 24, Exchange Online issues resulted in some users being unable to sign in and/or get their email in a timely manner for most of the day." It's still a miracle that quakes likes this one only occur once a few months. The biggest potential problem is getting compromised and then struck by a well prepared attack. Downtime for diagnostics, patching and then Restoring from a backup on the public cloud scale would be disastrous for the business. Just like having troops in tight formations (GoogleApps, Office 365, etc) public clouds put every one of its members in jeopardy of one deadly blow. How many times credit card databases got stolen over the last 15 years? Bottom line: private clouds are safer, more evasive and easier to repair (think a small group of gorilla fighters vs legions of shoulder to shoulder clone-army), besides it's very unattractive for top-notch hackers because there's not much gain in hacking in.