after having some weird issues with Sessions and ZEO usage I've found out part of the problem. It turns out certain browsers (IE6 mostly) save the session ID cookies, but sometimes these disappear. This results in a new _ZopeId being generated and thus the new session is empty.
At first i thought it was a session product problem, but in recreating this with my own session management (mysql based) the same issue arises.
I don't know why this happens, the only obstacle I'm facing now is to create an adequate solution ;)
The cookie approach should work. You should be able to set persistent cookies on the client browsers (unless the browser has cookies disabled, in which case you should tell the user that they must enable cookies if they want to proceed). If you can't set persistent cookies then it could be due to a cross-browser scripting problem (ie. you are setting a cookie within an iframe that is loaded from a third-party site) or you are not setting the appropriate fields in the cookie to make it persistent. You should try to investigate the cause of the "cookie disappearance" (use a tool to look at the http headers that are sent/received). If you can't get cookies to work then you need to give users unique links (ie. embed their id in an html link) or force the users to log in. Jonathan