It is great for DR if it can support your IO load, considering the cloud sucks for IO. :)

One project moved from AWS to a managed hosting provider with gear built to our specs mostly due to IO issues... continued to grow and then went back to AWS looking to do an easy DR process. Had some issues just with EC2 being able to keep up with replication at that point.

The one thing I'd like to try with AWS though is their Direct Connect service. Basically colo in a facility near them and get a cross connect to EC2 (think it focuses on VPC). http://aws.amazon.com/directconnect/

IO loads on real hardware, EC2 for all the other stuff.