You would normally have your own Mountain Lion server which would be accessible via the Internet so it could push updates to remote users. If you don't want to have a Mountain Lion server in your office you could have this hosted at a datacenter for you.
Two example companies that will let you do this are as follows -
Apple with Lion and Mountain Lion have used much the same technology as previously used for iPhones to provide management capabilities and this explains how Profile Manager can manage both Macs and iOS devices.
As iOS management like this has existed for longer than for Macs, there are more third-party solutions available to manage iOS devices using the same interfaces. The developers of (mainly PC) management software are still catching up.
There are some aspects you can manage already 'in the cloud' for Macs, for example distributing software to Macs. Google's Sapien software can run on Google's App Engine and someone has managed to get Caspar running on Amazon's EC2 service. See http://www.justinrummel.com/jamf-software-casper-suite-in-an-amazon-ec2-cloud/
I may be unaware of some solutions, but my feeling is that at the moment if you want something that can fully manage Macs you need to still at some level include Apple's tools as part of that solution.
(Centrify needs to be installed in to your AD setup which for most people rules out the cloud, nor can it by itself push to remote users unless they are connected to AD.) Caspar covers much but cannot (according to that blog) do everything from the cloud.