Continuations used to be used more on news.yc but it was trivial to flush the cache by making a few requests from a single client causing everyone's sessions to be hosed. That causes a switch to URL parameters for lots of things; why not all things? It's a fundamentally flawed model that I've never seen pg defend. It's certainly not scalable. Either the server stores info for all N clients, which fails for large N, or you give each client their own piece of info to store.