Personally, I've never been a huge fan of having someone else control my mission-critical data. I would never recommend a purely cloud EHR like PracticeFusion to anyone.
AC Cloud is great for smaller practices and they do give you the ability to return to an on-premise installation if needed. LogMeIn is a great example. It started off free and they just kept increasing the price. For us IT people who used Central to manage computers. The price went from $300/year to over $30,000/year in just a few years. Every year the price would double and then triple. We got out when the price was hitting $5,000 a year. We found an app that was able to be self-hosted and never looked back.
Cloud is great for auxiliary services like email, VoIP, etc. But I wouldn't want to be at the mercy of the cloud provider for my mission-critical data. AC is still leaps and bounds above most other cloud-based EHR's with the ability to switch back to on-premise.