Isn't it going to affect performance to have your server talking to your DB over the internet (as opposed to a local network which I presume is the case when running EC2 instances in the same availability zone)?
I thought this but after doing some tests the results are pretty negligible.
A windows 2008 server license on 2 machines for fall back comes in at around £700 - £800 a month per instance. The same redundancy on Azure is around £80 - £100 a month. If it doesn't work then we go back to the drawing board, if it does work then we have saved ourselves an almighty chunk of money.
We cache a lot of data in our application too which we are putting into elasticache, which is local to EC2.
We haven't used it in great stress yet but initial tests were very good
A majority of our writes are product updates but they are done directly into azure from a local box. These can't be done from AWS as they go into gbs but that is the only situation we need worry about.
If azure opened it's model up then we wouldn't need to do all this!