Ease of exit
I don't use any cloud services personally, I look after an Ubuntu instance on AWS and some S3 buckets for CD for a client. It was set up by someone else.
All my eggs are in one basket on a server in my garage (next to some old rags and cans of petrol). Backups are cool, I have heard of them. I think I have some somewhere.
My point is that once one starts to rely on a third party, more and more of ones business systems tend to become dependant on that third party. Eventually the cost of transition may become prohibitive.
MS know this as do Google and Amazon.
Now if MS, Google and Facebook can work together to find a nice file format to download all ones social media outpourings in order to import into another social media service. Why can't the big cloud/SaaS providers do the same?
I might then consider their usefulness for storing, deploying and serving information that I don't mind finding its way into the public domain.
As a kid I got stuck in a clothes spin drier, I was on the verge of panic before I escaped.
I don't like being trapped.... Cloud SaaS all stink of entrapment.