So basically we can now replace the painful SQS with hosted Redis! Yayy!
RE: Mongo. If you're using EC2 for MongoDB you're most likely doing it wrong. Not sure if there is much written about the Foursquare problem out there, maybe I'll get around to writing about it, one day. Pretty much the only company that I know off doing bullet-proof, scalable and fast Mongo hosting is http://objectrocket.com/. There's a reason Rackspace acquired them. Unless you're able to get placement of your SSD loaded servers in the same datacenters as Amazon, go with them. It's well worth your time to not muck around with Mongo.