IdentityMap stores the model in memory for the process. Only storing for the lifetime of a request wouldn't be terribly useful. IdentityMap will be extremely u

IdentityMap stores the model in memory for the process. Only storing for the lifetime of a request wouldn't be terribly useful. IdentityMap will be extremely useful for the majority of sites since they have very low traffic, processor, and memory demands, and therefore it's unlikely you'll have too many processes running using up their own memory containers. Though you could argue these sites really don't need additional caching anyways (they'd still respond slightly faster with IdentityMap). For high traffic sites it'll still be useful to save some trips, but you'll also want to implement and manage a distributed cache (for models, actions, fragments, etc). It's available and sort of works now. You just have to turn it on and be mindful of how associations are handled. Still a work in progress.