OK, caker disputes what Guspaz/I said about the meaning of AWS's availability zones. From a couple minutes of Googling, it seems to be consistent to "data center", but Amazon is unwilling to actually use those 2 words. In any case, what I said about AWS occasionally experiencing region-wide outages is true.
Back on topic, TheClient, nobody really provides guarantees, and even when they do, such guarantees are of questionable value. The bottom line is, any decent company does the best they can, and mostly succeed, but nobody is perfect and everybody suffers occasional, unexpected outages. Edit: You might find how companies *respond* to outages more interesting. Amazon has a reputation for poor communication during outages, and IMO Linode could do better there too, but both of them post good RFOs afterwards. And that's not even getting into how well and quickly they resolve problems, and what measures they take to prevent them from recurring.
Hurricane Electric (Fremont)'s power situation aside, Linode and the data centers it uses have acceptable (i.e. excellent) track records. I imagine the same is true for AWS. They are both good platforms to build reliable services upon, but in both cases you have a responsibility to build the level of reliability you desire. For example, to work around a Linode or EC2 host failing, have two VPSes in an HA configuration. To work around a data center power outage, have VPSes in multiple data centers/availability zones. To work around single nuclear attacks, use multiple AWS regions (Linode's data centers are all far enough apart). To work around large-scale nuclear war, put them on different continents, though such an event would probably cause widespread power, Internet and life outages for your users, making your service's reliability irrelevant. To workaround Rackspace acquisitions, use both Linode and AWS at the same time.
Edit: As for large customers, I'm unable to provide a list, but a Linode employee might chime in. (Or another user who feels like digging up one of the lists previously given.)
Edit: My NTP server has hundreds of thousands of users, possibly a couple million over the course of a month. Do I count?
