Hehe, I've had personal experience at running an Exchange installation, not a job for the faint of heart I would agree that any enterprise level servie like this will take _major_ investment of physical & intellectual resources.
We looked at third party hosted Exchange offerings and decided they were too expensive and of questionable reliability (company's too small to trust). We chose a Microsoft hosted Exchange because we assume they have the physical & intellectual resources to run data centers correctly (they have mutliple spread out globally, maybe not on the Google scale but plenty enough). At the moment here in Australia our closest M$ data center is in Singapore. There is a major push on to get one located on our continent at the time of writing.
(Incidentaly, ancedotaly it seems Apple's iCloud is having a lot of trouble with up time, perhaps no better than its old Mobile Me days.)
Redundancy? Because M$ have a native application (Outlook) we have a physical copy of all our email, calendars, contacts & data files on every PC, Mac, Android & iPhone. The Mac's have time machine setup to maintain constant versioned backups of everything on them to a NAS. The PC's do simillar with a cobbled together solution.
Assuming that every M$ data center in the world is not hit simultaneously by earthquakes & sunami's and our office burns down at the same time and all of our phones/tablets are all stolen as well at the same time.. we should be ok.. :-/ I think i just tempted the gods
Correct me if I'm wrong but with Google's system there is no native app's therefore no offline access to data except maybe your phone? Its all in the cloud baby.. and they reserve the right to rummage through all your data looking for advertising opportunities?
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