If the service you chose, for instance, starts to go south on a regular basis, and you've built your entire ecosystem inside a specific vendor's cloud, you could be in a world of hurt.
This right here is why I don't use cloud services and do everything I can to make them unattractive to the users. The more "investment" made into a given cloud system, the more "pain" received when the cloud goes down. As things currently stand, that means I don't trust the cloud for anything other than basic commodity services that can be easily replicated by a number of cloud providers.
My experience also tells me that I am a small fish and I possess very little leverage when I deal with the cloud providers. When things go south, I am not big enough to get anyone to care so I am forced to "take what they give me". Worse, my only recourse is to take my business elsewhere, which is why my comment above is so important.
All in all, it's just not a good deal for anyone that values control. If I were a shop with little to no IT skills, I could overlook the loss of control as the payoff for not requiring an IT dept is hard to pass up. However, just as soon as you sign up and do that -- now what? Who is going to "drive" your IT dept and make your IT better tomorrow than it is today? The cloud provider? Ha!