The needs of our customer are too transient for reserved yet, so it's primarily been as needed (on demand?) We run into problems during provisioning sometimes and Amazon has to then raise our quota. Some customer architecture and capacity requirements have stabilized, so they are talking about getting reserved instances. We also have been experimenting with provisioning a bunch of servers for short durations for "burst processing" of content, but we're never totally sure if AWS will have the capacity we need. Things like reserved instances might get more use by us soon.