Interesting tidbit in the announcement: Data between the US-East-1 and US-East-2 regions is priced at the lower inter-AZ rate ($0.01 per GB, or half price). That's pretty great if you're looking to add a layer of regional redundancy.
But it's only a penny, right? How much could it matter? It actually matters a lot. At both my previous and current employers, a surprisingly large portion of our hill comes from data transfer across AZs. All the microservices, all the memcache hits, and all the database replication add up quickly.