The first and obvious detractors are the people who write custom software.
This is kind of weird, because there will always be the need for custom software – not every problem can be solved with a scalable, generic, solution over the cloud.
Same goes for “on-premises software” solutions vendors.
But there are some valid arguments against using the cloud (mainly for business, but private use of Facebook, Twitter, LinkedIn, GoogleApps, Apple iCloud, MicroSoft, Amazon, etc are all in the same basket).
Your ISP (Internet Service Provider), your telephone company, and the media companies, end up owning you cloud data in a lot of cases.
They claim they are agnostic, that they keep no personal data, but when push comes to shove, they generally will cave in and give up your private data to anyone with a big enough stick.
They also control your access. Putting your faith in the cloud means you’re also putting all your faith in continued, unfettered access.
This access might start at a low enough introductory cost, but you need to know that it might not be cheap forever.
Your frog might find itself boiling in future… reasonable sounding upgrades and cost escalations might land you in an expensive monthly plan that you can’t afford to continue, yet can’t afford to leave.
Some legal advisors are warning about “who owns your data?”, “Who owns your customers?”, and “Who owns the data you are storing online?”.
The Intellectual Property of your business may turn out to be owned by the software company, or the hosting company, or some third-party PaaS provider in Slovenia or Fiji or Ireland.
These issues are by no means resolved, and you may not want to be a test-case for resolving them.
On the matter of which country your cloud is in, there’s also the question of which Taxation Jurisdiction it falls under. What do you need to know if you are paying tax in, for example, Isle of Man?
The Cloud is a bit like the Wild West… you know that it’s going to turn out OK, but you don’t know where the next gun-slinger is coming from, or if he has his eyes on your local store.
Some aspects of your business do not have a “transition path” into Cloud. For example, if you want to move your financial systems into the Cloud, you have only one option – to completely replace your current system. That’s not a simple undertaking, and it’s NOT fault-tolerant.