[kls]

Sorry for replying to my own post but I did want to touch a little further on this subject. above I stated:

So if the client wanders off, you have no way to clean up based on that event other than a brute force timeout.

A common rebuttal to this is well just sprinkle in an AJAX call. Which in my opinion is the worst decision one can make. Now not only are you supporting a server model but you also have client mode sprinkled in which compounds the complexity of you application significantly, in essence doubling your technology stack. This is the choice a lot of developers make when trying to dabble in RIA and it is my held belief that this is a fatal mistake. It doubles the required skill set and creates convolution in the sequences of application communication.

[mhansen]

By 'an AJAX call', do you mean having the client periodically ping the server, and then cleaning up the session if the ping times out?

[kls]

No I mean wire an event to the unload of the page, that notifies the server that the client has abandoned the app.