Ongoing Continuations compares passing state in hidden form fields or server-side sessions with continuations:

"What David’s afraid of, and with good reason, is the obvious alternative: storing all of the data as global session state, with each page (or a cookie) referencing a single session ID from which the rest of the information can be retrieved on the server side. The problem with this, as Gilad points out, is that in the world of back buttons and tabbed browser, there is no single session state: the same user in the same session might be simultaneously exploring two booking options, and the server can easily get confused between them. Encoding the information in hidden fields on the page means that the server’s idea of the current state always matches the user’s."