"A prolonged, ongoing Gmail outage has some Google Apps administrators pulling their hair out as their end users, including high-ranking executives, complain loudly while they wait for service to be restored."

"However, a major concern and objection to SaaS applications is their performance and availability, since they're provided by the vendor via the Internet and accessed by end users through browsers. When the applications become slow or altogether unavailable because of problems in the vendors' data centers, IT administrators have little to do but sit and wait for the problem to be fixed."

http://www.computerworld.com/action/article.do?command=viewArticleBasic&articleId=9117322

That means the core issue is that administrators become users. After all, how different is this than when a system within the data center becomes unavailable? People thru out the company have little to do but sit and wait. It is the same thing. And this is the reason why arguments against SaaS often fall short.