Since http is stateless, web applications should probably be too. The "flash" concept for temporary storage for messages or other data between requests works well as long as requests are made in the anticipated order but has the potential to go out of date or clog the session when they are not. fadingflash is intended to address this problem.
fadingflash provides a storage that will automatically expire after one request unless it is explicitly kept.
fadingflash depends on beaker to provide a session.