In what way does fsync work differently in the cloud?
In case your traffic is huge, this can cause big problems that are very hard to fix. And it did cause problems for Reddit, as EBS is notoriously awful in this regard (and others, like big latencies on access).
Basically when working at big scales, nothing beats having complete control over your infrastructure. It may be tough and time consuming, but at least you can identify the problem and fix it.
It is my opinion that something like Google's search cannot be built on top of Amazon's AWS.
Google can't exist (well) on top of AWS as AWS is designed for the deployment of (qusi)stateless applications. Saying that you can't build a data intensive application on top of it is like saying that your machinegun sucks at grating cheese.
OVM was designed to run a search engine origionally (darkmatr, now defunct due to lack of comparitive profitability), so you could quite easily build google on top of it. It wouldn't surprise me if google would work really well on top of that stack.
http://teddziuba.com/2011/04/amazon-the-purpose-of-pain.html